I think she just used me

So here is this girl,I know her since sem 1(we are in 6th sem now) we were just normal friends. I had always helped her whenever she asked for any kind of help and support. But I realized the change in her behaviour today(which I should have realized at the beginning of 5th sem) - whenever I text her for a help,she responds after one day and says idk. Neither does she pick calls. I sincerely helped her all through. Today I asked for a favor and she stated a demand in return, I said I can't ,then she again started to ignore. What to do ????