Well, if you are sick of it but do not want to confront her, then just make excuses to not to help her. After a few times, she will get the message. We can't always expect others to return favor, but sometimes helping others can make yourself happy as well (I think it feels better to help others than ro receive help). Though if you are getting sick of it, then stop. Any relationship between two human beings is a two-way road; you can't always be the one who gives.
I had a friend that always ask me for help with math but always left me alone when she had other friends around. It felt like the only purpose she came to me was to get help with math. I felt like I was being used and I started making excuses (too busy, not sure), and eventually she got the message and stopped. I kind of confronted her before but she didn't get it at first.