Seems to me Annette was seriously interested in the professor. (Spoiler
Obviously, if Frankie hadn't gotten mad and started hitting on the hungarian, it wouldn't have ever come up.
But when Annette starts hanging out with the professor, it appears she's sincerely offering him her virginity at one point.
That's not the sign of someone just trying to make Frankie jealous. (Which is what she claims at the end.)