I know a good fiddle teacher in Dallas. It would be best for your friend to buy a fiddle with the help of a good fiddle teacher (my friend does not sell them, but can help your freind choose). If you want more detail, PM me.

There are good places to buy fiddles from. And it may be wise for your friend to rent one for a while, if she's a beginner. If she's not, then she can find good instruments at Ebay or at local stores. Try Mars (they're going out of business and great deals), Try some of the other music stores (phone book, look for chains, they have more stock).

There are good jams around town. I don;t know any that are disciplined about Old Timey stuff, they say the Denton Town Hall jam is pretty much bluegrass - the Sons of Hermann Hall jam on Thursday nights is a real mixed bag, and quite spectrum of playing skill too. There are others, mostly singer oriented sessions or Celtic tune sessions.