Mi hermana quiere desvestirse pronto, ponerse el pijama y dormir temprano.

In Spanish, possessive adjectives like mi, tu, su, nuestro normally go directly before the noun without an article.

So you say:

• mi hermana = my sister
• mi casa = my house

Not:

• la mi hermana ✘

English uses my the same way, so this part is actually quite similar.

Because querer is commonly used with another verb in the infinitive to mean to want to do something.

Pattern:

• querer + infinitive

So:

• quiere desvestirse = she wants to get undressed
• quiere ponerse el pijama = she wants to put on her pajamas
• quiere dormir = she wants to sleep

This works much like English want to + verb, except Spanish uses the infinitive directly and does not need a separate word like to in English.

That -se marks them as reflexive verbs.

In this sentence:

• desvestirse = to get undressed
• ponerse = to put on, to get oneself dressed in something

The idea is that the subject is doing the action to herself.

So:

• Mi hermana quiere desvestirse = My sister wants to get undressed
• Mi hermana quiere ponerse el pijama = My sister wants to put on her pajamas

The reflexive pronoun is se here because the subject is ella / mi hermana.

Both are possible.

You can put the reflexive pronoun:

1. attached to the infinitive

   • quiere desvestirse
   • quiere ponerse

2. before the conjugated verb

   • se quiere desvestir
   • se quiere poner

Both mean the same thing.

In your sentence, the infinitive-attached form is used because it is very common and neat when several infinitives are listed together:

• quiere desvestirse, ponerse el pijama y dormir temprano

Because dormir is normally not reflexive when it simply means to sleep.

• desvestirse = to undress oneself
• ponerse = to put something on oneself
• dormir = to sleep

So only the first two need a reflexive pronoun here.

There is also dormirse, but that means to fall asleep, not just to sleep.

Compare:

• quiere dormir temprano = she wants to sleep early / go to sleep early
• quiere dormirse pronto = she wants to fall asleep soon

Spanish often uses the definite article (el, la, los, las) instead of a possessive adjective when talking about clothing, body parts, and personal items, especially when it is obvious whose item it is.

So Spanish prefers:

• ponerse el pijama

rather than:

• ponerse su pijama

Both can be grammatical, but el pijama sounds more natural here because we already know it is your sister’s pajamas.

This is a very common Spanish pattern:

• Me lavo las manos = I wash my hands
• Se pone el abrigo = He/She puts on his/her coat

This is a very common question because both can relate to time, but they are not the same.

• pronto = soon
• temprano = early

So here:

• desvestirse pronto = to get undressed soon
• dormir temprano = to sleep early / go to bed early

A useful way to think about it:

• pronto answers how soon?
• temprano answers at what time, relative to normal?

Examples:

• Voy pronto. = I’m going soon.
• Me acuesto temprano. = I go to bed early.

Because in Spanish, just like in English, one verb like quiere can govern several infinitives in a list.

So this structure means:

• she wants to get undressed, to put on her pajamas, and to sleep early

Spanish does not need to repeat quiere before each infinitive.

You could repeat it for emphasis, but it would sound less natural in a normal sentence:

• Mi hermana quiere desvestirse, quiere ponerse el pijama y quiere dormir temprano.

That is correct, but unnecessarily repetitive.

The sentence contains a list of three actions:

1. desvestirse pronto
2. ponerse el pijama
3. dormir temprano

In Spanish, as in English, items in a list are separated by commas, and the last item is introduced by y = and.

So:

• desvestirse pronto, ponerse el pijama y dormir temprano

That is the standard punctuation pattern.

Yes. It is natural Spanish.

Spanish often uses dormir temprano where English might more naturally say:

• go to sleep early
• go to bed early
• sometimes sleep early

The exact English translation depends on context, but the Spanish itself is normal and idiomatic.

If you want to be more specifically go to bed early, Spanish often says:

• acostarse temprano

So:

• dormir temprano = sleep/go to sleep early
• acostarse temprano = go to bed early

That is exactly the connection.

• poner = to put
• ponerse = to put on oneself / to put on

So:

• poner el libro en la mesa = to put the book on the table
• ponerse el pijama = to put on pajamas

The reflexive form often changes the meaning from a general action to something done to oneself.

This is very common with clothes:

• ponerse una chaqueta = to put on a jacket
• quitarse los zapatos = to take off one’s shoes
• vestirse = to get dressed
• desvestirse = to get undressed

Yes, you could, but the nuance is slightly different.

• desvestirse = to get undressed
• quitarse la ropa = to take off one’s clothes

They are very close in meaning.

In this sentence, desvestirse sounds compact and natural because it matches the sequence of bedtime actions well:

• get undressed
• put on pajamas
• sleep early

If you used quitarse la ropa, it would still be correct:

• Mi hermana quiere quitarse la ropa pronto, ponerse el pijama y dormir temprano.

Yes, it sounds natural in Spain.

A couple of notes:

• pijama is standard in Spain.
• The whole sequence sounds normal for bedtime.
• Spain Spanish and Latin American Spanish would both understand and use this sentence easily.

If you wanted an even more everyday bedtime verb, many speakers might also say:

• acostarse temprano = to go to bed early

But your original sentence is completely natural.