Unless you are in a hurry, you are on your own at the sporting goods store. They are going to recommend a 31 or 32 they have in stock based on her weight.
You need to tell her HC and parents what you are thinking and have her tryout some bats in practice or loan them to you for a week.
I think you need to get a better sized bat first then try to nail down a make and brand.
I saw online to have her hold the bat with one hand/arm out in front of her horizontally. If she can hold it for 25 seconds without much movement, the weight is good. Does that sound like a decent test?
There's a Miken Freak (white with scroll writing) on closeoutbats.com for only $100. It was $300 a few years ago. I own a 30" for my 9yr old. Its an awesome bat. If you can find your size, don't hesitate.
FYI... don't waste your money with anything less than a 31"
Try and find a store that will let you demo bats.
there is one around us about 45 mins away but still a great help that way she can swing them hit with them before you buy one even if its not the same model.