Learn Hardcore Chinese: bié dānxīn, nǐ fàngxīn, tā yíhuìr jiù huílái. - Don’t worry; relax

别担心 = “don’t worry” (a prohibition/command: stop the worrying).
你放心 = “rest assured” (a directive to relax). Putting them together is natural in Chinese for comfort and emphasis, like saying “Don’t worry—really, relax.” You could also soften it with particles: 别担心了，放心吧。

What’s the difference between 别 and 不要 when telling someone not to do something?

Both can mean “don’t,” but:

别 + V is shorter, more colloquial, often more direct: 别担心.
不要 + V can sound slightly more formal or gentle: 不要担心 (often feels like “no need to worry”).
If you want “stop doing (an ongoing action),” 别…了 is very common: 别担心了 (“stop worrying now”).

Are 担心 and 放心 antonyms?

More or less, yes.

担心 (dānxīn) = to worry, be anxious. Common patterns: 为/对 + X + 担心 (“worry about X”), e.g., 为她担心.
放心 (fàngxīn) = to feel at ease / set one’s mind at rest. Common patterns: 让/使 + 人 + 放心 (“put someone at ease”), e.g., 这消息让我放心. As a command, 放心 means “don’t worry; relax.”

How is 一会儿 used? Does it mean “for a while” or “in a moment”?

Both, depending on context:

Point in time (soon): 她一会儿就回来 = she’ll be back in a moment.
Duration (for a short time): 等一会儿 = wait for a bit; 玩儿一会儿 = play for a while. Related words:
马上 = right away, immediately (stronger).
很快 = soon (general).
一下 = for a sec / once (often softens a request: 看一下 “have a quick look”).
过一会儿 = after a little while.

Why the “r” sound in 一会儿 (yíhuìr)? Do I have to say it?

That “r” is 儿化 (erhua), common in the North (e.g., Beijing).

Mainland writing often uses 一会儿, but many Southern speakers pronounce it without the “r” (yíhuì) and may also write 一会 informally.
Both pronunciations are understood; follow your teacher’s/local model.

Why is 一 pronounced yí in yíhuìr?

Tone sandhi:

一 is normally first tone (yī).
Before a fourth-tone syllable, it becomes second tone: yí + huì (since 会 is fourth tone).
Before 1st/2nd/3rd tones, it usually becomes fourth tone (yì), e.g., yì tiān (天 is first tone).

What does 就 do in 一会儿就回来?

就 here signals quickness/sooner-than-expected/immediacy. It turns “in a moment” into “in just a moment.”

Without 就: 她一会儿回来 (neutral “she’ll be back in a bit”).
With 就: 她一会儿就回来 (sooner, reassuring).
Contrast: 才 gives the opposite (later than expected): 她一会儿才回来 (“not until a bit later”).

Where does 就 go in this structure? Could I say “她就一会儿回来”?

Use: Subject + time expression + 就 + verb.

Correct: 她一会儿就回来 or 一会儿她就回来.
“她就一会儿回来” is unnatural because 就 typically links to the following verb phrase, not to the time phrase after it.

Why is it 回来 and not 回去 or just 回?

回来 = come back (toward the speaker’s/current location).
回去 = go back (away from the speaker’s/current location).
回 usually needs an object to say where: 回家, 回公司. Without an object, 回来/回去 are the natural intransitive choices in motion grammar with direction.

Do I need 了 after 回来? What’s the difference between 就回来 and 就回来了?

You don’t need 了 here, but it changes nuance:

她一会儿就回来: She’ll come back soon (neutral reassurance).
她一会儿就回来了: She’ll be back any minute now (imminent/arrival-as-a-change-of-state).
Also, without the time phrase: 她回来了 means “She has (now) come back.”

Is this considered future tense even though there is no 会?

Yes. Chinese doesn’t require a future marker. Time words (一会儿) and adverbs (就) are enough to place it in the near future.
You could say 她一会儿就会回来, but it’s unnecessary and can feel heavier. For “about to,” 就要/快要…了 is also common: 她快要回来了.

Can I move the time phrase to the front: 一会儿她就回来?

Yes. Both orders are fine:

她一会儿就回来 (subject first; very common in speech)
一会儿她就回来 (time-first; also natural)

Is 放心 a verb or an adjective here? Does it need an object?

Here 放心 functions as a verb in the imperative (“put your mind at ease”). It’s commonly used intransitively: 你放心.
To specify what, use patterns like:

为/对 + X + 担心: 别为她担心 (“don’t worry about her”).
让/使 + 人 + 放心: 这件事让我放心 (“this puts me at ease”).
Negative state: 放心不下 (“can’t set one’s mind at ease about…”): 我对她放心不下.

How do I specifically say “Don’t worry about her” using this sentence’s words?

Use 为/对…担心:

别为她担心。
别担心她。
Both are natural; 为她担心 is a bit more explicit/formal.

Any pronunciation tips for the whole sentence?

别担心: bié (2) dān (1) xīn (1)
你放心: nǐ (3, half-third before 4) fàng (4) xīn (1)
她一会儿就回来: tā (1) yí (2) huì(r) (4) jiù (4) huí (2) lái (2)
Keep the 儿化 light if you’re not used to it; in many regions people simply say yíhuì.

Could I drop 你 and just say 别担心，放心?

Yes, in context that’s fine and common in speech. Including 你 directly addresses the listener and can feel a bit more personal/emphatic: 你放心.

How would I make it more polite or formal?

Use 您: 您放心.
Add softening particles: 别担心了，您放心吧。
In very polite/register-neutral reassurance: 不用担心，您尽管放心。