Several answers on this site suggest addressing a woman as 大姐 but that seems wrong for a professor speaking to a woman student. To be clear, by professor here I mean a university professor speaking to a university student. The term professor in English is more specific than 老師 in Chinese.
The situation would be speaking to a student in class, or in office hours, or when meeting them on campus, when it is not a student that I have worked closely with. In the US I normally address students in this situation as Mr or Ms.
Would it be best to use the student's full name with no title?
On the difference between teacher and professor, in both US usage and UK, see
I almost left out any mention of not using 小姐. It now well known that this is not good on the mainland.