yàoshi míngtiān hái bù hǎo, tā jiù děi zài yùyuē yīshēng.

要是 means if. It introduces a condition:

要是 + condition, (就) + result

In everyday speech, 要是 is very common and a little more conversational than 如果. In this sentence, you could also say:

如果明天还不好，她就得再预约医生。

That would mean basically the same thing.

Chinese often omits a repeated subject when it is already obvious from context. So:

要是(她)明天还不好，她就得再预约医生。

Both are natural. The sentence leaves out 她 in the condition clause because the second clause makes it clear who we are talking about.

For learners, it may feel easier to include the subject at first, and that is completely fine.

Here 还 means still or yet.

So 还不好 means:

• still not well
• not better yet
• still not recovered

This is a very common pattern:

还不 + adjective/verb

For example:

• 还不懂 = still don’t understand
• 还没来 = still hasn’t come

In this sentence, 还不好 refers to her condition not having improved by tomorrow.

In health-related contexts, 好 often means to get better, to recover, or to be well.

So:

• 好了 = got better / recovered
• 还没好 = not better yet
• 不好 = not well / not better

This is very natural in Chinese. Even though 好 often means good, in sentences about illness or health it commonly refers to recovery.

就 marks the result that follows from the condition. In English, it is often like then, in that case, or simply part of the natural flow of if..., then....

So the pattern is:

要是...，就...

In this sentence:

• 要是明天还不好 = if she’s still not better tomorrow
• 她就得再预约医生 = then she’ll have to make another appointment with the doctor

Sometimes 就 is not translated directly, but it makes the Chinese sentence sound natural and clearly links the two parts.

Here 得 is pronounced děi and means have to, must, or need to.

So:

她就得再预约医生 = then she’ll have to make another appointment with the doctor

This is a very important word because 得 can have different pronunciations and meanings:

• děi = must / have to
• de = structural particle
• dé = to get / to obtain, or part of certain complements

In this sentence, it is definitely the modal verb děi.

再 is used for again in the future or for an additional action that has not happened yet.

Here, the re-booking is something she may need to do later, so 再 is correct:

再预约医生 = make another appointment / book again

By contrast, 又 is often used for something that has already happened or is being viewed as a repeated event:

• 她又来了。 = She came again.
• 你又忘了。 = You forgot again.

So in this sentence, 再 fits because the new appointment is still in the future.

Yes, in this context 预约医生 means make an appointment with the doctor.

Chinese often does not need a separate word equivalent to English with in this kind of phrase. The verb 预约 can take the person or service directly.

So these are all possible depending on context:

• 预约医生
• 预约看医生
• 跟医生预约
• 预约门诊

In your sentence, 预约医生 is a compact and natural way to express the idea.

Yes. That version is also natural:

她要是明天还不好，就得再预约医生。

Chinese often allows some flexibility with where time words and subjects appear, as long as the sentence stays clear.

The original sentence starts with the condition first:

要是明天还不好，她就得再预约医生。

Your version starts with the subject first:

她要是明天还不好，就得再预约医生。

Both are good. The difference is mostly about emphasis and flow, not basic meaning.

明天 appears early because time words in Chinese usually come before the main description of the action or state.

So:

要是 明天 还不好 literally feels like: if tomorrow still not better

This is normal Chinese word order. Time is often placed before the verb or adjective it relates to.

Other natural arrangements are also possible, such as:

她明天要是还不好，就得再预约医生。

But in all of them, 明天 comes before the part describing whether she is better.

A useful way to see the structure is:

要是 + condition, subject + 就 + 得 + 再 + verb + object

Applied to this sentence:

• 要是 = if
• 明天 = tomorrow
• 还不好 = still not better
• 她 = she
• 就 = then
• 得 = has to
• 再 = again
• 预约医生 = make an appointment with the doctor

So the overall pattern is:

If [condition], then [someone] has to [do something again].

This sentence is a good example of how Chinese stacks several small function words before the main verb to build meaning.