Он готов ждать у входа, лишь бы сестра спокойно закончила краситься.

Yes. Он готов ждать means he is ready/willing to wait.

In Russian, готов + infinitive is a very common pattern:

• Я готов помочь. — I’m ready to help.
• Она готова уехать. — She’s ready to leave.

In this sentence, готов does not just mean physically prepared; it often means willing to do something.

So:

• Он готов ждать у входа = He is willing to wait at the entrance.

Notice that готов agrees with он:

• готов — masculine
• готова — feminine
• готово — neuter
• готовы — plural

Because ждать is the imperfective verb, and it fits the idea of being in the process of waiting or being willing to wait for some time.

Compare:

• ждать — imperfective, to wait
• подождать — perfective, to wait for a while / to wait until something happens

After готов, Russian often uses an infinitive that describes the activity in a general way:

• Он готов ждать — He is prepared to wait

If you said готов подождать, that would also be possible in some contexts, but it would sound a bit more like:

• He’s willing to wait a bit
• He doesn’t mind waiting for a while

Here ждать is the more neutral choice.

У входа means by the entrance / near the entrance.

The preposition у usually means by, near, next to, and it takes the genitive case:

• вход — nominative
• у входа — genitive after у

So:

• ждать у входа = wait by the entrance

Compare:

• у двери — by the door
• у окна — by the window
• у дома — by the house

You could also see на входе in some contexts, but that usually sounds more like at the entrance area or depends on the exact situation. У входа is the most natural choice for standing/waiting near the entrance.

Лишь бы means something like:

• as long as
• if only
• provided that

It introduces the one condition that matters.

So the sentence means:

• He is willing to wait at the entrance, as long as his sister can calmly finish putting on her makeup.

This expression often carries a feeling of:

• that’s all I care about
• that’s the only condition

Examples:

• Лишь бы он пришёл. — As long as he comes.
• Лишь бы не было дождя. — As long as there’s no rain.
• Лишь бы успеть. — If only we make it in time.

So in your sentence, he doesn’t mind waiting — the important thing is that his sister finishes peacefully.

This is a very important Russian pattern.

After бы, Russian normally uses the past-tense form of the verb, but the meaning is often hypothetical, desired, or dependent, not actual past time.

So:

• закончила here is not really simple past
• it is the form used with бы to express something like:
  • so that she could finish
  • as long as she finishes
  • if only she would finish

This is similar to how Russian forms the conditional/subjunctive:

• Я бы пошёл. — I would go.
• Она бы пришла. — She would come.

In your sentence:

• лишь бы сестра спокойно закончила краситься means roughly
• as long as his sister calmly finishes/can finish putting on makeup

So the -ла form is required because of бы, even though the meaning points to something not yet completed.

Because сестра is the subject of the clause introduced by лишь бы.

The structure is:

• сестра закончила краситься

Here:

• сестра = the one doing the action
• therefore it is in the nominative case

If it were the object, then you might expect сестру, but it is not the object here.

Breakdown:

• сестра — subject
• закончила — verb
• краситься — infinitive complement

So:

• лишь бы сестра закончила... = as long as the sister finished...

Russian often omits possessive words like his, her, or my when the meaning is obvious from the context.

So:

• сестра can mean the sister or his/her sister, depending on context

If the sentence is already about он, then many speakers would naturally understand сестра as his sister.

Russian does this a lot:

• Он поднял руку. — literally He raised hand, but naturally He raised his hand.
• Она закрыла глаза. — She closed her eyes.

If you wanted to emphasize it, you could say:

• лишь бы его сестра спокойно закончила краситься

But without его, the sentence is still perfectly natural if the relationship is clear.

Краситься has a few meanings depending on context. Here it means:

• to put on makeup
• to do one’s makeup

So:

• закончила краситься = finished putting on makeup

Yes, in other contexts краситься can also mean:

• to dye one’s hair
• more generally to color oneself / be painted

But with a sentence like this, especially involving спокойно закончила, the most natural reading is finish doing her makeup.

Related verbs:

• красить — to paint/color something
• краситься — to put on makeup / dye one’s hair / color oneself

Examples:

• Она долго красится. — She takes a long time doing her makeup.
• Она красит волосы. — She dyes her hair.

Because the action is directed toward oneself.

Russian often uses reflexive verbs for actions people do to themselves:

• мыться — to wash oneself
• одеваться — to get dressed
• бриться — to shave
• краситься — to put on makeup / dye one’s hair

So краситься is not exactly to paint oneself word-for-word in normal usage, but that reflexive idea is still there historically and grammatically.

In this sentence:

• закончила краситься literally feels like
• finished making herself up

Because закончила краситься focuses on finishing the process.

Compare:

• накраситься — to put makeup on / to get made up
• закончить краситься — to finish putting makeup on

These are close, but not identical.

накрасилась emphasizes the result:

• she has done her makeup

закончила краситься emphasizes the endpoint of an ongoing activity:

• she finished doing her makeup

In your sentence, that process-oriented meaning fits well, because he is waiting while she is still busy.

Спокойно is an adverb meaning:

• calmly
• peacefully
• without stress or interruption

It modifies how she finishes doing her makeup:

• спокойно закончила краситься = finished putting on her makeup calmly / without being rushed

In context, it suggests something like:

• he is willing to wait outside, just so she can finish in peace

So спокойно adds an emotional nuance, not just the bare fact of completion.

Yes, Russian word order is flexible, but the original order sounds natural.

Original:

• Он готов ждать у входа, лишь бы сестра спокойно закончила краситься.

This order presents:

1. what he is willing to do
2. the condition that matters

You could rearrange parts for emphasis, for example:

• Лишь бы сестра спокойно закончила краситься, он готов ждать у входа.

That puts more emphasis on the condition first:

• As long as his sister can finish her makeup calmly, he is willing to wait at the entrance.

You could also move спокойно around a little:

• ...лишь бы сестра закончила спокойно краситься but that is less natural here than the original.

So the given version is both natural and stylistically smooth.

It is generally neutral to slightly conversational and very common in everyday Russian.

It is not slang, and it is not especially formal. You can hear it often in spoken Russian.

Depending on tone, it can sound:

• practical: as long as...
• emotional: if only...
• slightly impatient: just let... / so long as...

In this sentence it sounds natural and idiomatic.

Not with exactly the same meaning.

• чтобы usually means so that / in order that
• лишь бы means as long as / if only / provided that

Compare:

• Он ждёт у входа, чтобы сестра спокойно закончила краситься.
  This sounds odd, because it suggests he is waiting at the entrance in order for his sister to finish, which is not the intended relationship.

• Он готов ждать у входа, лишь бы сестра спокойно закончила краситься.
  This means he is willing to wait, provided that his sister can finish peacefully.

So лишь бы is the right conjunction for the idea of the only condition that matters.

The tone is fairly natural and slightly expressive. It suggests patience and consideration:

• He doesn’t mind waiting
• the important thing is that his sister gets to finish calmly

There may also be a faint nuance of:

• He’ll put up with the inconvenience
• as long as she can finish in peace

So the sentence is not just factual; it also shows attitude.