xiūxi le liǎng tiān yǐhòu, tā de shēntǐ zhōngyú hǎozhuǎn le.

This 了 marks the action 休息 as completed: she rested for two days.

So 休息了两天以后 means after resting for two days.

A useful pattern is:

verb + 了 + duration + 以后
= after doing something for a certain amount of time

Examples:

• 学了三年汉语以后 = after studying Chinese for three years
• 等了一个小时以后 = after waiting for an hour

Without this 了, the sentence may sound less clearly focused on the completed rest period.

The second 了 shows a new change of state: her condition has improved / ended up improving.

So the two 了's do different jobs:

• 休息了两天: marks the resting as completed
• 好转了: marks that a change happened, from not improving to improving

This is very common in Chinese. One sentence can contain more than one 了, because each one may belong to a different part of the sentence.

Before measure words, Chinese usually uses 两 rather than 二.

So:

• 两天 = two days
• 两个小时 = two hours
• 两个人 = two people

Using 二天 is usually unnatural in standard Mandarin.

A simple rule:

• use 二 for counting, numbers, math, phone numbers, dates, etc.
• use 两 before measure words

Since 天 is acting as a measure word for days here, 两天 is the natural form.

以后 means after or afterward.

In this sentence, it attaches to the earlier action and creates a time phrase:

休息了两天以后
= after resting for two days

It tells us that the main event happened after that rest period.

A common structure is:

[event/time] + 以后, ...
= after [event/time], ...

Examples:

• 吃饭以后再去 = go after eating
• 下课以后我回家 = after class, I go home

Chinese very often puts time information before the main clause.

So this order is very natural:

休息了两天以后，她的身体终于好转了。
Literally: After resting two days, her body/health finally improved.

This is similar to English phrases like:

• After two days of rest, ...
• Once she had rested for two days, ...

Chinese often goes from background/time first, then the main result.

好转 means to improve, especially in a condition such as:

• health
• illness
• symptoms
• a situation that had been bad

So here it means her physical condition got better.

It is slightly more formal and specific than just 好了.

Compare:

• 好了 = got better / recovered / became okay
• 好转了 = showed improvement, turned for the better

For illness or medical recovery, 好转 is very common.

Both can work, but they are not exactly the same.

• 她终于好转了 focuses on her overall condition
• 她的身体终于好转了 focuses specifically on her body/health

Chinese often uses 身体 when talking about health recovery. It sounds natural and clear, especially in contexts involving illness, weakness, or recovery.

So 她的身体终于好转了 is a bit more explicit:

• not just she in general
• but specifically her physical condition

的 marks possession or association.

So:

• 她 = she
• 她的 = her
• 她的身体 = her body / her health

This is one of the most basic uses of 的: noun/pronoun + 的 + noun

Examples:

• 我的书 = my book
• 他的老师 = his teacher
• 她的身体 = her body / her health

终于 is an adverb meaning finally or at last.

In Chinese, adverbs usually come before the verb they modify.

So:

• 终于好转了 = finally improved

This is the normal placement.

Compare:

• 她终于来了 = she finally came
• 天气终于暖和了 = the weather finally became warm

So the pattern is often:

subject + 终于 + verb + 了

Yes, sometimes you can, but the nuance changes a little.

• 休息了两天以后 clearly emphasizes that the two-day rest was completed
• 休息两天以后 can still be understood, but it may sound less explicitly tied to a completed event

In this sentence, 了 is very natural because the rest period is a completed action that happened before the improvement.

So for learners, 休息了两天以后 is the safer and more standard choice here.

Yes. In 两天, 天 functions as a measure word meaning day(s).

Chinese often uses time words directly as measure words:

• 一天 = one day
• 两天 = two days
• 三年 = three years
• 四个月 = four months

So you do not need another measure word between 两 and 天.

Yes, 之后 could also work here:

休息了两天之后，她的身体终于好转了。

This means almost the same thing: after resting for two days, ...

In many contexts, 以后 and 之后 are interchangeable.
Very roughly:

• 以后 is extremely common and flexible
• 之后 can sound a bit more formal or slightly more written in some contexts

But in this sentence, either is fine.

Yes. 终于 often suggests that:

• the result was delayed,
• there was difficulty before it happened,
• or people had been hoping for it.

So 终于好转了 does not just mean improved. It means something like:

• finally improved
• improved at last

That gives the sentence an emotional sense of relief or long waiting.