Сколько бы раз я ни проверяла подгузник ночью, мне всё равно кажется, что малышка вот-вот проснётся.

This is a fixed concessive pattern meaning no matter how many times... or however many times....

So Сколько бы раз я ни проверяла... does not ask an actual question. It sets up the idea that the result stays the same regardless of the number of times.

You can compare it with:

• Кто бы ни пришёл... = Whoever comes...
• Что бы ни случилось... = Whatever happens...
• Где бы он ни был... = Wherever he is...

In this construction, бы and ни normally work together.

• бы helps form this hypothetical/indefinite concessive meaning
• ни reinforces the idea of no matter...

So Сколько бы раз я ни проверяла... is a standard Russian pattern.

Using не instead of ни would be wrong here.
This is one of those structures that is best learned as a whole:

• сколько бы ... ни
• кто бы ... ни
• что бы ... ни
• где бы ... ни

After бы, Russian uses the -л form, which looks like the past tense form, but here it does not literally mean past time.

So я ни проверяла here means something like:

• however many times I may check
• no matter how many times I check

The form also shows the speaker’s gender:

• проверял = male speaker
• проверяла = female speaker
• проверяли = plural

So проверяла tells you the speaker is female.

With numerals and quantity words like сколько, Russian uses a special counting form:

• один раз
• два раза
• пять раз
• сколько раз
• много раз

So раз here is the normal word in counting expressions meaning times.

This is slightly irregular, so it is worth memorizing as a set phrase: сколько раз = how many times.

It is in the accusative case, but for an inanimate masculine singular noun, the accusative looks the same as the nominative.

So:

• nominative: подгузник
• accusative: подгузник

That is why it looks unchanged.

The verb проверять takes a direct object, so подгузник is exactly what you would expect here.

Ночью is a very common adverbial form meaning at night or during the night.

It comes from the instrumental case, but in practice you can often learn it as a set time expression:

• утром = in the morning
• днём = in the daytime
• вечером = in the evening
• ночью = at night

По ночам would mean at nights / night after night / habitually at night, with a stronger repeated-habit sense.

Here ночью is natural because it refers to the nighttime situation in general.

Literally, мне кажется means it seems to me.

Russian often uses the dative for the person experiencing a feeling, impression, or perception. So:

• мне кажется = it seems to me
• мне холодно = I am cold
• мне интересно = it is interesting to me

In this sentence, мне кажется is softer and more subjective than я думаю.
It suggests an uneasy feeling or impression rather than a firm opinion.

Here всё равно means still, all the same, or nevertheless.

It shows that the result does not change:

• she checks the diaper many times
• but she still feels the baby is about to wake up

So the sense is: Even after all that, the feeling remains the same.

This is different from another common use of всё равно meaning it makes no difference / I don’t care.
Russian uses the same phrase in both situations, so context matters.

Вот-вот means any moment now, just about to, or on the verge of.

It creates a strong feeling of immediacy. The speaker feels the baby may wake up literally in the next second.

Common examples:

• Поезд вот-вот придёт. = The train is about to arrive.
• Он вот-вот упадёт. = He is about to fall.
• Дождь вот-вот начнётся. = The rain is about to start.

It is a very natural, slightly vivid, everyday expression.

Проснётся is the future of the perfective verb проснуться.
It refers to one complete event: to wake up.

That works well with вот-вот, because the speaker expects one imminent event: the baby is about to wake up.

If you used просыпается, that would suggest:

• is waking up right now, or
• wakes up habitually

That is a different idea.

So:

• вот-вот проснётся = is about to wake up
• просыпается = is waking up / wakes up

Малышка is an affectionate diminutive meaning something like little one or baby girl.

It tells you two things:

1. the child is female
2. the tone is tender and affectionate

Compare:

• малыш = little one / little boy / baby
• малышка = little girl / baby girl
• ребёнок = child, more neutral

So малышка adds warmth and a family, caring tone.

It has three main parts:

1. Сколько бы раз я ни проверяла подгузник ночью
   = concessive subordinate clause: no matter how many times I check the diaper at night

2. мне всё равно кажется
   = main clause: it still seems to me

3. что малышка вот-вот проснётся
   = content clause after что: that the baby is about to wake up

That is why there are commas:

• one after the first subordinate clause
• one before что

So the sentence moves like this:

No matter how many times X, it still seems to me that Y.

Yes, Russian word order is flexible, but the current order is very natural.

Starting with Сколько бы раз я ни проверяла... puts emphasis on the repeated checking first. That sets up the contrast before the main point: despite all that, the anxious feeling remains.

A different order is possible, but this version sounds smooth and expressive:

• first the repeated effort
• then the unchanged feeling
• then the feared result

So the word order helps the emotional flow of the sentence, not just the grammar.