If she's not sure she can make this decision at the interview.
Most likely, during interview would cause more delay. A background check has to be done on her current name and new name. If she files form with new name now, USCIS can perform the check before the interview. If she does it on the day, they'd have to run this check and it will take some time.
Name change in most cases means no same day oath, as far as I know. It doesn't matter ask for it now on form or during interview.