Getting reinfected with pink eye is NOT uncommon an allergies would not be my first guess.
When I was in junior high, I don't know how but I got pink eye. I'd never even heard of it before a friend started freaking out that I had it. Didn't know how contagious it was, either. So I was sent down to the nurse's station who didn't take me seriously, figuring I was trying to get out of class or something because they hadn't had a case of pink eye in over ten years. However, one look at me and she also freaked and sent me straight home.
I was out of school for weeks with a visit back to school for a day or two here and there before being shuffled back home. I kept giving myself pink eye because I was always rubbing my eyes, so I'd transfer it from one eye to the other back and forth. It always started red and swollen before it developed into the crusty grossness. Finally after constantly treating both eyes, it went away. So I went back to school, only to find out that about one in 12 kids was home sick with pink eye, too. Then I'd get it again from school. Back to the meds. Finally cleared up. Back to school. Oops! Pink eye again! Back home and on the meds. ARGH! That happened THREE times before I was either diligent about NOT touching my face (I'm always rubbing or scratching something or moving hair off my face) or somehow the contagion was contained.
Thankfully that's the only time in my life I've had pink eye and I have allergies and rub my eyes all the time so I wouldn't expect the two are related or I'd have pink eye all the time.
Lesson learned? Pink eye is EXTREMELY contagious and it's easy to get reinfected. I'd keep treating her eyes and if you do take her to an allergist, make sure you let them know she's had pink eye so it doesn't spread.