Part of the problem here is the unequal levels of power the two people have. Her big gun, is that if he continues this low level but objectionable behavior is to file an official complaint.
The number and range of things the professor, who is her advisor, can do, is vast. She could end up taking years longer to finish her degree. Advisors have the p;otential for great interference in her career.
If he does this at any other times, she might look for a high ranking friend (male or female) to pull him aside and mention that he’s pretty obvious in his looks and that the professor is risking a HR complaint.
The situation sucks.