Not sure what to do

I have a friend that is driving me up the wall. She was a good friend for awhile, but now I'm not so sure. It seems that everytime we go to the store or something like that she wants to go out to lunch and most times she wants me to pay for her lunch. She pays after I've paid for one, but I just can't go out to lunch all the time. Her and her husband make alot less money than my family and she borrows from her mother's overdraft account. (Her mother is in a nursing home.) I don't understand how she can just use her mothers money like that. If I can't afford to go out to lunch or get a pedicure I stay home, but she borrows from someone that can't even give her permission. It is also such a one sided friendship. I drive everywhere. She has a car and yet she never will drive. She says that her car is too old to drive too often. It's a 91 toyota so I know it's fine. I really wish I knew more of what to do. I don't want to write her off because I know that will not help her (she's been on anti-depressents for over 13 years plus anxiety meds and she said she's bi-polar. I don't believe that one). I think I've decided that I will let her come to me. If she wants to be my friend then she needs to make the effort. I've made alot of the effort, (even inviting her to a girls night where she wanted to bring her husband and was mad when I said no husbands) and I think it's her turn to try.