At 14 1/2, I would say she is too young to use MSN and look at web pages unsupervised. Sucks, but given that there is no real censorship on the internet, then that's how it is for teens. Especially with MSN, even programs like NetNanny and other content control programs can't really stop her chatting with complete strangers on MSN.

I'd give her maybe 1-2 hours a night on school nights, once homework / chores are done, and maybe longer on weekends, but make sure that family/social commitments come first. Don't forget to encourage physical activity as well, of course...*grin*