The jock doesn't owe anybody an apology. He has a girlfriend, and that girl knows it so she had no business asking him to go to prom.
"Good" girls like her end up with a "broken heart" (Judy's term), because they chase that which they have no business chasing.
Judge Judy's line - "You learned a really good lesson. There are a lot of nice guys out there. You just have to look really hard." - is pure fail. I have no doubt that there are plenty of "nice guys" that would have gladly taken her to prom and she wouldn't have to look hard at all to find them. Somehow she felt entitled to the school's star athlete who is already hitched.
At 16 years old, one knows better. The real lesson is for her to grow up and not cry when she's unsuccessful at stealing other girl's boyfriends. Furthermore, don't be stupid with your money by spending $900 on a prom dress. The girl and her parents are idiots.