Should I let my 13 yr old start baby sitting?

I have been looking for a baby sitter job for my daughter and came across that site. I am a little nervous about having my 13 year old watching some other peoples kids. Does anyone have any young teens that baby sit? Is it alright to let a 13 yr old start to baby sit?  She really wants to earn some money and I don't really have a good argument with why she cant but it still makes me nervous. Thanks for listening :)