tuìshāo yǐhòu, tā juéde shēntǐ hǎo le yìdiǎnr, xīnqíng yě qīngsōng duō le.

Yes, 退 originally has the idea of to move back / recede / subside. In 退烧, it means the fever goes down or subsides.

So 退烧 is a very natural Chinese way to say:

• the fever went down
• to recover from a fever
• to no longer have a fever

It does not mean someone is physically stepping backward. In medical or everyday health contexts, 退 is often used for symptoms decreasing, like something receding.

以后 means after. It comes after the event it refers to, so:

• 退烧以后 = after the fever went down

This is a very common Chinese pattern:

• 吃饭以后 = after eating
• 下课以后 = after class ends
• 回家以后 = after going home

So the structure is:

• [event] + 以后

In this sentence, 退烧以后 sets the time frame for what follows.

Yes. 退烧后 and 退烧以后 are both natural.

• 退烧后 = after the fever went down
• 退烧以后 = after the fever went down

In many contexts, they are basically interchangeable. A rough feeling is:

• 后 can sound a little shorter and slightly more compact
• 以后 can sound a little fuller or more conversational

But in this sentence, either works well.

Because 退烧以后 is a time phrase placed at the beginning of the sentence. In Chinese, when a longer time phrase or background phrase comes first, it is very common to separate it with a comma:

• 退烧以后，她……

This helps show:

• first, the time/background
• then, the main statement

It is similar to English punctuation in sentences like:

• After her fever went down, she felt...

觉得 means to feel, to think, or to find. Here it introduces her personal perception:

• 她觉得身体好了一点儿
  = she felt her body/physical condition was a little better

It makes the sentence subjective: this is how she felt, not necessarily a formal medical judgment.

You could compare:

• 她身体好了一点儿 = her physical condition improved a little
• 她觉得身体好了一点儿 = she felt that her physical condition improved a little

The second sounds more personal and experiential.

Yes, 身体 literally means body, but in Chinese it also often refers to physical health or physical condition.

So:

• 身体好 can mean healthy / physically well
• 身体不好 can mean in poor health / not feeling well
• 身体好了一点儿 means her physical condition got a little better

This is very common in Chinese. It does not just refer to the body as a physical object.

The 了 in 好了 marks a change of state. It shows that something has become different from before.

• 身体好 = the body/health is good
• 身体好了 = the body/health has gotten better / is better now

So here:

• 身体好了一点儿 = her physical condition became a little better

This 了 is very important, because without it the sentence would sound less clearly like a change from a previous condition.

一点儿 means a little. Here it shows a small degree of improvement.

So:

• 好了一点儿 = got a little better

This pattern is common:

• 快了一点儿 = a little faster
• 贵了一点儿 = a little more expensive
• 舒服了一点儿 = a little more comfortable

In this sentence, 一点儿 softens the statement. It suggests she is better, but only slightly.

In everyday Mandarin, 一点儿 is extremely common and very natural, especially in Mainland Standard Mandarin.

You will also see or hear:

• 一点
• 一点儿

Both can occur, but 一点儿 is especially standard in speech for a little / a bit.

So here:

• 好了一点儿 sounds very natural

If you say 好了一点, many speakers will still understand it, but 一点儿 is the safer and more standard form for learners in this kind of sentence.

也 means also / too.

The sentence first says:

• her physical condition got a little better

Then it adds:

• her mood also became much more relaxed

So 也 connects the two improvements:

• 身体好了一点儿，心情也轻松多了
• Her body felt a little better, and her mood also became much more relaxed.

It shows that not only her body improved, but her emotional state improved as well.

多了 after an adjective means much more or a lot more.

So:

• 轻松 = relaxed
• 轻松多了 = much more relaxed

This is a very common pattern:

• 好多了 = much better
• 舒服多了 = much more comfortable
• 方便多了 = much more convenient

It often implies a comparison with an earlier state, even if that comparison is not stated directly.

Here, it means her mood was noticeably more relaxed than before.

They are both about degree, but they show different amounts of change.

• 好了一点儿 = got a little better
• 轻松多了 = became much more relaxed

So the sentence suggests:

• physically, she improved somewhat
• emotionally, she improved quite a lot

This contrast is very natural. Chinese often uses different degree expressions in the same sentence to show nuance.

The 了 in 轻松多了 also points to a change compared with before.

• 轻松多了 = much more relaxed now than before

This structure often appears as:

• Adj + 多了

Examples:

• 好很多了 is possible in some contexts, but 好多了 is much more common
• 清楚多了 = much clearer
• 精神多了 = much more energetic

So the second 了 is not random. It helps express that her mood has changed into a more relaxed state.

Because Chinese often avoids repeating words when the meaning is already clear.

Fuller version:

• 她觉得身体好了一点儿，觉得心情也轻松多了。

But this sounds repetitive. So Chinese naturally says:

• 她觉得身体好了一点儿，心情也轻松多了。

The second part is understood as continuing the same perspective: it is still what she feels.

This kind of omission is very common in Chinese.

In Chinese, 轻松 can describe both:

• a person feeling relaxed
• a mood feeling relieved or relaxed

So 心情轻松 is very natural and means something like:

• in a more relaxed mood
• emotionally relieved
• less burdened mentally

It does not have to mean cheerful or happy in a big, excited way. It often suggests that stress, worry, or pressure has eased.

Yes, that is grammatically possible:

• 心情也轻松了一点儿 = her mood also became a little more relaxed

But it changes the nuance.

• 轻松多了 = much more relaxed
• 轻松了一点儿 = a little more relaxed

So the original sentence makes her emotional improvement sound stronger than her physical improvement.

A simple way to see it is:

• 退烧以后 = time/background
• 她觉得身体好了一点儿 = first main idea
• 心情也轻松多了 = second main idea

So the pattern is:

• After [event], she felt [change 1], and [change 2] also happened.

More literally:

• After the fever went down, she felt her physical condition was a little better, and her mood was also much more relaxed.

This is a very typical Chinese sentence pattern:

1. time phrase first
2. person
3. feeling/perception
4. result or changed state
5. another parallel clause with 也