Learn Hardcore Chinese: tā yǐqián zhù zài Běijīng.

Not necessarily. 以前 just says the action/state was true in the past; it’s neutral about the present.
To make “no longer” explicit, add a change-of-state: 她以前住在北京，现在不住了。
For stronger “once (but not now)” feel, use 曾经: 她曾经住在北京（现在不住了）。

Why is 在 used after 住? Can I just say 住北京?

住在 + place is the standard, safest form: 她住在北京。
住 + place (e.g., 住北京) is common in speech (especially in the north) but is less formal and not always accepted in careful writing or tests.
With detailed or longer locations (addresses, compounds), 住在 + place sounds better: 住在中关村北大街20号.
With pronouns and very short locations, both often occur: 住你家 / 住在你家.

Can I put 在北京 before the verb? Is 在北京住 okay?

Yes. Both patterns are fine:
- 她住在北京。 (default)
- 她在北京住。 (puts light focus on the location)
When adding complements (duration, frequency), fronting the location is very common:
- 她在北京住了三年。
- 她以前在北京住过。

Do I need 了 or 过 to show the past?

No. Chinese often uses time words like 以前 to anchor time. 她以前住在北京 is already past.
Use 过 for past experience: 她在北京住过。
Use 了 for completed events or to state duration/endpoints: 她在北京住了三年。
Don’t say 她住在北京了 to mean “lived in Beijing (past)”; that’s not how 了 works here.

Is 住过在北京 correct?

No: 住过在北京 is ungrammatical.
Correct options:
- 在北京住过。
- 住过北京。 (acceptable, but the first is more common/natural)

How do I negate this?

Habitual/state in the past: 她以前不住在北京。
A specific past situation/window: 她以前没住在北京。
To contrast past and present: 她以前住在北京，现在不住了。
Both 不 and 没 can work with 以前, but they differ in aspect: 不 = general/habitual; 没 = didn’t (actual occurrence).

What’s the difference between 以前, 之前, 从前, and 曾经?

以前: before/previously (general, neutral). Can be absolute or relative to a reference time.
之前: more explicitly relative; usually tied to a reference point or event: 出发之前.
从前: “long ago/once upon a time,” storytelling/literary tone.
曾经: adverb “once/at one time,” often implies “not now”; pairs naturally with 过: 他曾经在北京住过。

Can I move 以前 to the very beginning?

Yes: 以前她住在北京。 This topicalizes the time frame, giving it slightly more emphasis.
Punctuation pause (comma) is optional in writing: 以前，她住在北京。

What is 在 doing here compared with 在 used for progressive aspect?

Here 在 is a preposition marking location: 住在北京 = “live at/in Beijing.”
Progressive 在 precedes a verb to mean “be in the middle of doing”: 她在吃饭 = “She is eating.”
So in 住在, 在 links the place; in 在吃, 在 marks aspect.

How do I say “She has lived in Beijing before” (experience) vs “She used to live in Beijing” (past state)?

Experience: 她在北京住过。/ 她以前在北京住过。 (at least once; doesn’t say how long)
Past state/habit: 她以前住在北京。 (a prior residence, neutral about now unless you add context)

Pronouns: 她 and 他 are both pronounced tā—how do I know the gender?

Any tone or pronunciation tips for this sentence?

Pinyin: tā yǐqián zhù zài Běijīng
Tones: 她(tā1) 以前(yǐ3 qián2) 住(zhù4) 在(zài4) 北京(Běi3 jīng1)
Keep the two fourth tones in zhù zài crisp without turning the first into a rising tone.
There’s no special third-tone sandhi here (only the usual “low” realization of a third tone before a non-third tone).

Can I say 她以前在北京 to mean she was in Beijing (not necessarily lived there)?

Yes: 她以前在北京。 = She was in Beijing before (could be traveling, studying, etc.).
To specify residence, keep 住: 她以前住在北京。

Are there more formal or alternative verbs to 住在?

住: everyday verb for “live/reside.”
居住: formal/literary; use 居住在/于北京 (both are fine).
生活在: “to lead one’s life in,” more about life in a place than just address; slightly literary/emotive.
住于: rare/literary in modern usage; prefer 居住于 if you need formal style.

How do I add duration or endpoints?

Duration with 了: 她以前在北京住了三年。
Experience with duration: 她以前在北京住过三年。 (implies a three-year stint sometime before)
Until a time point with 到: 她以前在北京住到2019年。