⟩ Sometimes we get involved with a client and have to stay later than scheduled. Would that be a problem for you?
There are limits to the questions that can be legally asked in a job interview. An interviewer can't ask you how many kids you have, if you have a car or any other personal questions. But that doesn't mean you should try to hide pertinent information because it will only backfire on you down the road.
You are building a relationship with a manager that you hope to work for. Don't start your beauty career off on the wrong foot. Tell her what she needs to know for the good of the salon.
The best is answer is "No mam, that would not be a problem for me. I understand that it is easy to get tied up servicing a client and there will be times I need to stay to help the salon."