I bought an Alpine Micro for my girlfriend and she seems to like it. She even picked it out. It shoots pretty well, but like you said it is not the best bow on the market. However it was only 190 dollars. If you want better you need to jump up to the 300-400 dollar mark or higher.
Hers is set up at 30 lbs of draw at 25 inches of draw length. It will shoot a 286 grn 1813 aluminum jazz arrow at 189 fps. I would like to know what weight arrow was used with the browning to get 280 fps. I have a bowtech mighty might that has an IBO speed of 322. At 26 inches of draw and 51 lbs I get 244 fps with a 315 grn arrow. If you buy a browning I would not expect to see numbers any where near that with your wifes set up.
Does the speed matter that much though? What is she intending on doing with it? Is she going to hunt or shoot 3-D competively? If not I would not worry about the speed, it has nothing to do with how well she can shoot the bow or how much fun you can have with it. If anything some of the faster bows might be harder to shoot.
We looked at a hoyt rintec when we were shopping and it is a great little bow! As would be the bowtech you are talking about. The rintec was 299 at my shop, and I don't know what the miranda goes for. They also have a rascal I believe which I think they said was around 400, I could be remembering it wrong though.
How much money are you looking to spend and how serious is she about it? There are a few really nice bows that would fit her rather than going the youth bow route. They just are not very inexpensive is all. I would suggest going with the alpine or a genisis to begin with. And in a few years if she is really into it throw down the cash for something nicer.
The parker challenger is another good bow for you to look at. Or even a genisis Pro.
I would probably get her a 40 lb peak weight bow and turn it all the way down to begin with. My girlfriend struggles a little with 30 lbs on her bow.
Look at this link.
Another link.
Good luck with what ever you decide. Just make sure she is happy. I would have picked the rintec hands down if it was my choice, but my girlfriend liked the alpine. She shot the browning as well.
Paul