How much should I charge somebody for computer lessons?

My English teacher has a Vista laptop, but she is totally computer illiterate. She can turn her computer on, but that's about it. She wanted to hire me to teach her all the basics, such as e-mail, Microsoft Word, things like that. (The poor woman doesn't even know how to cut and paste). So I was wondering how much I should charge her per hour. I was thinking about 10 dollars because I didn't want to seem stingy, but I know I can teach her a lot of stuff in one hour. I haven't charged people before so I have no idea what normal rates are. Any suggestions?