Hi M.,
As parents, we know our children best. And because of that, maybe you anticipate her needs and "answer" her requests before she actually verbalizes them. I used to do that. Who am I kidding--I still do!!! lol But this could be a factor in why she acts differently at school.
I'm proud of you for allowing this test even though it sounds like you're not really for it. This means you're open to doing what's best for your daughter, which can be difficult if it's not our idea. Perhaps you should ask the county to test her at your home AND at school so they can give you insight into why she acts so differently. This would be good for you, your daughter and her teachers.
Before the evaluator comes, prepare your daughter so she welcomes them. Get her excited that someone new will come to the house and explain to her beforehand what to expect from them. Act as if this is a treat, because it truly is. Even if they say she's "delayed", you're getting this info early so you can help guide your daughter and bring her up to speed. And if they say she's fine, go ahead and insist she gets tested at school so everyone can figure out what the major difference is. Perhaps it's the school and you should know. (I'm not suggesting anything sinister here, just that maybe they could do more for the children in their care.)
Good luck and have fun with this. You never know, the evaluator may be a good friend down the road!!
D.