I'm sorry no one responded to your post. Is this still happening. It's impossible to say what might be causing this. It could simple be she got an irritant in her eye, or could be she is getting conjunctivitis in that eye, could be she has scratched it...could be allergies causing this.
If it is bothering her, which it appears to be, then she should be seen by a Vet.
We took her to the vet and they coukdnt find anything significantly wrong so they have us a few antibiotics and her eye has improved thanks for the concern
They didnt mention anything about conjunctivitus and its gotten better so i dont believe it could be that. Shes about 6 and loves being outdoors and has never had the problem before. Her eye cream seemed to helo snd its healing.