Babysitting friends baby.

My friend wants me to babysit her daughter. She's almost five months old. She just got a job and she said she would pay me. I'm kind of a pushover so I'm nervous that she'll say she 'doesn't' have the money and I'll say it's okay.

I would like some money though. Babysitting is the only thing I'm good at. And I feel bad that my husband is the only one bringing money in. (Even though he says staying home is better than paying for daycare) I can even take our daughter when I babysit. She's almost 3 months.

Anyway, should I babysit for her for free? Or should I charge her? If so, how much?