Helping out friend but friend won't reciprocate

I have a dear friend living on the edge of poverty that I want to help financially. Her car is somewhat dangerous to drive. It keeps stalling. She doesn't have the money to get it fixed, let alone buy something more dependable. I have the means to help her out. I told her that I would give her $3,000 to buy a car. My stipulations were to buy a certified used car (not any old thing advertised in the newspaper or Craigslist) and to clean my apartment once a month. She does house-cleaning on the side. She balked at the cleaning part of the deal saying that two Fridays of the month were already taken up with her cleaning job and that she didn't want to work any other weekends at all.

This really hurt my feelings. I'm not asking her to pay back the money, because I know she doesn't haven't the means to do so. Besides, I really want to help her out, because she's my friend. It took her a lot just to ask me for help. I thought that she would want to "work it off." I'm beginning to think that it will come between us if she doesn't clean my apartment in exchange for the money. She has cleaned my apartment before and it takes her less than 4 hours. I live within 20 minutes driving distance of her apartment and 10 minutes from her work. I understand that she's tired after work. I'm not saying what day or time she has to clean. That's up to her. I may be moving out of the area in a couple years, so she would be released from that obligation. Am I being unreasonable in insisting that she clean my apartment once a month for 3 years max in exchange for $3,000?

Just want some perspective...