Advice on beginner trumpets?

Like Greg, I'm recommending a cornet rather than a trumpet. It isn't so much a matter of weight as it is balance. I actually recommend a cornet for all beginners because of the bad habits that can be developed by young players who are trying to play with their arms overly extended. In your daughter's case I would think this could be even a greater issue. Nice used horns are hundreds less than new ones and can often be used while learning then sold for virtually the same price you originally paid. I really like used Olds Ambassador and Conn Director horns, and while they are plentiful enough for spare parts to be available a nice used Yamaha is hard to beat.

You shouldn't worry about the weight. There's minimal difference between horns' weights anyway. The great thing about trumpet is the left hand is only used as support. If you really wanted you could play perfectly fine with your right hand only. That said I'd just recommend a solid student model. Something like a Yamaha or Getzen student model would be ideal, although even these can be pricey. You could try checking on eBay and could probably find ones in decent condition for a few hundred bucks. Other than that your best bet is checking with your school to see if they have an school-owned instruments, or going to a music store and setting up a rent-to-own deal. Here's an example of a horn that I think might work. There are plenty of other offers on ebay for the same model, this is just an example. http://www.ebay.com/itm/Lightly-Used-Yamaha-YTR-2335-Brass-Bb-Student-Trumpet-with-Case-/140747316829?pt=Brass_Instruments&hash=item20c5319e5d#ht_500wt_1287