Might be the beef. Might be the vaccines. Best thing to do is take the beef back out of the diet for 4-6 weeks. See if she improves. If she does, then add beef back into the diet. If she gets itchy again, it's likely the beef. If she doesn't, it was most likely the vaccines.
Note that it is Spring time and she could also have environmental allergies as well.
If you suspect food intolerants, I strongly recommend testing with your vet or http://www.nutriscan.org
It will save time, money and anguish for both you and your dog.
Best of luck to you!