The most common and most likely answer to this crossword clue is the 6 letter word RETORT
I've seen this crossword clue in The Daily Telegraph
R
E
T
O
R
T
More clues leading to the result RETORT
- Reply in respect of something wrong in law
- Witty comeback in regard to wrongful act
- Stand in science class to give answer
- Answer — one required in experiment, perhaps?
- Still dealing with infringement
- Comeback concerning damaging wrong?
- Time to leave rejected pig’s foot in counter?
- “Margaret” or “Thatcher”? The answer lies within
- Error message ends: wrong answer
- Apart from one time, Del Boy, say, returned a bit of repartee
Buddy explains!

The straight part
We know that "Sally/that assists in the laboratory" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sally/that assists in the laboratory = retort.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does RETORT mean?
RETORT noun- A sharp or witty reply, or one which turns an argument against its originator; a comeback.
- To say something sharp or witty in answer to a remark or accusation.
- To make a remark which reverses an argument upon its originator; to return, as an argument, accusation, censure, or incivility.
- To bend or curve back.
- To throw back; to reverberate; to reflect.
- A flask with a rounded base and a long neck that is bent down and tapered, used to heat a liquid for distillation.
- A airtight vessel in which material is subjected to high temperatures in the chemical industry or as part of an industrial manufacturing process, especially during the smelting and forging of metal.
- A pressure cooker
- To heat in a retort.