Learn Hardcore Chinese: tā juéde měitiān zǒu lóutī shànglóu bǐ zuò diàntī gèng jiànkāng. - She feels that walking up the stairs every day is healthier than taking the elevator.

她觉得... = “She feels / she thinks (in her personal view) that…”
她想... often means “she wants to…” or “she intends to…”, though it can sometimes mean “she thinks…”. It’s less clearly about an opinion here.
她认为... is more formal and logical, like “she considers / she is of the opinion that…”.

In a casual sentence about health habits, 觉得 is the most natural choice to express a personal view.

Where can 每天 go in the sentence? Is its position fixed?

In the sentence:

她觉得每天走楼梯上楼比坐电梯更健康。

每天 (every day) is placed before the verb phrase 走楼梯上楼, and that’s the most common and natural position.

You could also see:

她每天觉得走楼梯上楼比坐电梯更健康。
(Focuses a bit more on “every day she feels/thinks…”)
她觉得走楼梯上楼每天比坐电梯更健康。
(Sounds awkward; 每天 doesn’t fit well here.)

The safest and most natural for talking about a daily action is:

她觉得每天走楼梯上楼…
or
她每天走楼梯上楼，她觉得这比坐电梯更健康。 (split into two sentences)

Why do we need both 走 and 上楼? Aren’t they both verbs about moving?

Yes, both are verbs, but they describe different aspects of the movement:

走 = to walk (the manner of movement)
上楼 = to go upstairs / go up a floor (the direction/goal of the movement)

So 走楼梯上楼 literally means “walk (by) the stairs to go upstairs”.
You can see it as:

走（楼梯） = walk, using the stairs
上楼 = go upstairs

Chinese often combines a manner verb + direction/result verb:

跑进去 = run in
走出来 = walk out
跳上去 = jump up (onto something)

Here, 走 + 上楼 works the same way.

What exactly does 走楼梯 mean? Could we just say 上楼梯 or 爬楼梯?

走楼梯 literally is “walk (using) the stairs,” i.e. take the stairs (on foot).

Native speakers might also say:

走楼梯上楼 – walk the stairs to go upstairs (your sentence)
走楼梯 – take the stairs (context usually clear)
爬楼梯 – literally “climb the stairs”; often used too, feels a bit more “effortful”
上楼梯 – is possible but much less common than 走楼梯 / 爬楼梯.

In daily conversation about health/exercise, 爬楼梯 and 走楼梯 are both common. Your sentence is perfectly natural.

Why is 上楼 after 楼梯 and not before, like 上楼楼梯?

Chinese word order is:

Verb (manner) + Object + Verb (direction/result)

So:

走（manner) + 楼梯 (object) + 上楼 (direction/result)

You can’t say 上楼楼梯; that breaks the usual pattern. The action is:

You use the stairs (楼梯) while walking (走),
and the result/direction of that action is going upstairs (上楼).

So 走楼梯上楼 is “walk (using) the stairs to go upstairs.”

How does the 比…更… structure work here? Why do we have both 比 and 更?

The comparison pattern is:

A 比 B （更）+ adjective

In this sentence:

A = 每天走楼梯上楼
B = 坐电梯
adjective = 健康 (healthy)
intensifier = 更 (even more)

So:

每天走楼梯上楼比坐电梯 更健康
Going upstairs by stairs every day is even healthier than taking the elevator.

About 更:

It is optional in many comparisons:
- 她觉得每天走楼梯上楼比坐电梯健康。 (acceptable)
- 她觉得每天走楼梯上楼比坐电梯更健康。 (more natural here)
更 adds a sense of “even more / to a greater degree”.

With adjectives like 健康, slang or casual speech often uses 更 to make the contrast stronger and more natural.

Could we say 她觉得坐电梯没有走楼梯上楼健康 instead of using 比?

You can, but the nuance changes slightly.

A 比 B 更健康 = A is healthier than B. (neutral comparison)
B 没有 A 健康 = B is not as healthy as A (sounds more like B is clearly worse).

So:

每天走楼梯上楼比坐电梯更健康。
→ Going upstairs by stairs is healthier than taking the elevator.
坐电梯没有每天走楼梯上楼健康。
→ Taking the elevator is not as healthy as going upstairs by stairs every day.

Both are grammatical; the 比-structure is more neutral and very common in textbooks.

Why do we use 坐电梯 for “take the elevator”? Doesn’t 坐 just mean “to sit”?

坐 does literally mean “to sit,” but in modern Chinese, it also commonly means “to take (a vehicle / mode of transport)”:

坐火车 = take the train
坐飞机 = take a plane
坐公交车 = take the bus
坐地铁 = take the subway
坐电梯 = take the elevator

You don’t have to actually be sitting; it’s just the conventional verb for riding/using these means of transport.

Why is it 更健康 and not 更健康的 at the end?

In this sentence, 健康 is used directly as an adjective (predicate):

A 比 B 更健康。
A is healthier than B.

You only need 的 if the adjective is modifying a noun:

更健康的生活方式 = a healthier lifestyle
更健康的身体 = a healthier body

Here, there is no noun after 健康, so we don’t add 的.
“更健康” functions like “(is) healthier.”

Can the subject 她 be left out in Chinese?

Yes, if the subject is clear from context, Chinese often drops it:

(Context: you were just talking about her.)
觉得每天走楼梯上楼比坐电梯更健康。

However, in a standalone sentence or in writing, it’s more natural and clearer to keep 她:

她觉得每天走楼梯上楼比坐电梯更健康。

If I want to talk about myself, is it okay to just change 她 to 我?

Yes. The structure stays exactly the same:

我觉得每天走楼梯上楼比坐电梯更健康。
I think walking the stairs upstairs every day is healthier than taking the elevator.

You can replace 她 with any person:

他们觉得… (they think…)
医生觉得… (the doctor thinks…)

What’s the difference between 每天 and 天天? Could we use 天天 here?

每天 and 天天 both mean “every day,” but:

每天 is more neutral and works in both spoken and written Chinese.
天天 feels more colloquial and sometimes emphasizes frequency or intensity (“day after day,” “all the time”).

In this sentence, you can say:

她觉得每天走楼梯上楼比坐电梯更健康。 ✅
她觉得天天走楼梯上楼比坐电梯更健康。 ✅ (slightly more colloquial/emphatic)

Both are natural; 每天 is the safer default.

What exactly is the role of 上楼 compared to just saying 走楼梯?

走楼梯: take the stairs (it doesn’t specify up or down)
上楼: go upstairs / go up a floor

By saying 走楼梯上楼, you are specifying that you take the stairs in the upward direction, i.e. “go upstairs by stairs.”

In everyday speech, people might shorten it depending on context:

我上楼都走楼梯。= When I go upstairs, I always take the stairs.
我一般走楼梯，不坐电梯。= I usually take the stairs, not the elevator. (direction understood from context)

Your sentence chose the more explicitform 走楼梯上楼 to make the situation very clear.