tā yíhuìr yòng shǒudiàntǒng, yíhuìr yòng tóudēng.

Here it means now... now..., at one moment... at another..., or sometimes... sometimes....

So the sentence is describing alternating actions:

• 一会儿用手电筒
• 一会儿用头灯

In natural English, this could be:

• She uses a flashlight for a bit, then a headlamp for a bit.
• She keeps switching between a flashlight and a headlamp.
• Sometimes she uses a flashlight, sometimes a headlamp.

Important: in this sentence, 一会儿 does not mean in a moment.

This is because of the tone-change rule for 一.

Normally, 一 is first tone: yī.
But when it comes before a fourth-tone syllable, it changes to second tone: yí.

Since 会 huì is fourth tone, 一会儿 is pronounced:

• yíhuìr

This is a very common rule:

• 一个 → yí ge
• 一次 → yí cì
• 一半 → yí bàn

So the spelling shows 一, but the pronunciation here is yí.

一会儿 is pronounced roughly as yíhuìr.

The 儿 here is part of an erhua ending, which means the final sound gets an -r coloring. It is usually not pronounced as a full separate er syllable.

So instead of saying something like:

• yí huì er

you usually say something closer to:

• yíhuìr

This -r ending is especially common in northern Mandarin and in standard spoken Mandarin for certain words.

Chinese often repeats the verb in paired patterns like this for balance and clarity.

So:

• 一会儿用手电筒，一会儿用头灯

literally has the structure:

• for a while use X, for a while use Y

Repeating 用 makes the sentence sound natural and symmetrical.

If you removed the second 用, the meaning might still be understood in context, but the full repeated pattern is the normal and clearer way to say it.

The pattern is:

Subject + 一会儿 + Verb + Object, 一会儿 + Verb + Object

In this sentence:

• 她 = subject
• 一会儿 = for a while / then / at one point
• 用 = verb
• 手电筒 / 头灯 = objects

So the sentence is built like this:

• 她 + 一会儿 + 用 + 手电筒
• 一会儿 + 用 + 头灯

This pattern is useful for describing someone who keeps changing actions, tools, or states.

For example:

• 他一会儿看书，一会儿看手机。
  He reads a book for a while, then looks at his phone for a while.

• 孩子一会儿哭，一会儿笑。
  The child cries one moment and laughs the next.

No. 一会儿 can mean different things depending on context.

Common meanings include:

1. for a short while

   • 等我一会儿。
   • Wait for me a moment.

2. in a little while / soon

   • 我一会儿去。
   • I’ll go in a little while.

3. In the pattern 一会儿……一会儿……, it means now... now... / one moment... the next...

   • 她一会儿用手电筒，一会儿用头灯。

So you should learn the whole pattern, not just the word by itself.

• 手电筒 = flashlight or torch
  Literally, it is a handheld light.

• 头灯 = headlamp or headlight worn on the head
  This is a light attached to the head, often with a strap.

So the sentence says she switches between:

• a flashlight in the hand
• a headlamp on the head

In writing, 她 specifically means she / her.

But in spoken Mandarin, 她, 他, and 它 are all pronounced tā. So if you only hear the sentence, you would not know from pronunciation alone whether it means:

• he
• she
• it

You know it is she here because the written character is 她.

Because the sentence is simply describing an action pattern, without focusing on completion or a specific resulting state.

• 了 often marks a completed action or a change of situation.
• 着 often emphasizes a continuing state.

Here, the sentence just presents a scene or habit:

• She uses a flashlight at one moment, then a headlamp at another.

No aspect marker is necessary.

Chinese often leaves aspect unmarked when the context is enough.

It usually suggests alternation over time.

So it is not just saying she uses both a flashlight and a headlamp. It suggests something more like:

• first one, then the other
• back and forth
• switching between the two

That is the main effect of the 一会儿……一会儿…… pattern.

Yes. 手电 is a common shorter spoken form of 手电筒.

So these both work:

• 手电筒
• 手电

The full form 手电筒 is a little more complete and dictionary-like, while 手电 is very common in everyday speech.

For example:

• 把手电给我。
  Give me the flashlight.

Both are natural, but the sentence you were given uses the full standard word 手电筒.