I've seen a number of auctions for 'academic' versions of Vegas on ebay. The fine print says that a K-12 student is eligible for this pricing and that the software is identical to the full retail version. I was thinking of buying a copy for my 5 year old who's in kindergarten ;). Any reason this would be a bad idea?
Elsewhere on this site is a list of licensed academic resellers. If the one you saw on eBay is on the list, you can go ahead and buy a copy for your daughter with little worry ;?)