I'd try not to worry about how she'll do ahead of time (unless of course she has an LD or needs accommodations etc - in that case you'll want to ask for the accommodations). If she does well, all will be well. If she tests lower than you'd anticipate based on her past testing or other things you know about her, don't take the "we only accept our own testing" from the school as an absolute. Write down your concerns, write down what you want, and send it all in to the school along with copies of her previous test results. If you don't get the answer you want from your school, forward it all on to your school district's administrative office (to the head of the gifted department if there is one). The one thing I've learned over the years is that in most school districts, no policy is set in stone, and chances are there are already legions of parents ahead of you who've advoceated for their children who haven't qualified for gifted programming, chances are some of them have been successful, and chances are if you have a child who's anywhere near DYS levels, most of those other parents were advocating with far lower scores. SO - don't be intimidated if you do have to ultimately appeal a decision based on a "low" group test score.
Best wishes,
polarbear