Welcome AlexsMom :-)
First try not to make yourself crazy... the fact that your DD's current teacher thinks accelerating her is a good idea is surely some indication that she's likely to pass the proficiency tests (which are on 2nd grade material, not 3rd grade, right?) Certainly practising any weaker areas between now and the test seems like a reasonable idea, given that you're clear 2nd grade isn't the place for her and that she will be fine in 3rd.
It's crossing a bridge before you come to it, but I'd suggest caution on this:
If that happened, I don't think we'd agree to subject acceleration. Heck, I don't think we'd agree to subject acceleration if DD passed only one of the 4 subjects. DD wants "to be in a class where I'm in the middle" (in every respect - the only thing she's said she would worry about if accelerated was whether she'd be the shortest kid), and subject acceleration (IME) would make her extremely conspicuous.
If that happened, she simply wouldn't have an option (in her current school at least) of being in a class where she'd be in the middle; you'd be choosing between different compromises. Being conspicuous by leaving one class to go to another might be a good swap, if it resulted in her not feeling conspicious in the class where she was being taught.
(Also, I'm admittedly at sea with US bureaucracy and sometimes it does seem bizarrely rule-bound, but supposing she passed at the 95% level in 3 subjects and only at the 87% level in the fourth. Would the school really not find a way to accelerate her if they knew that the alternative was having to manage subject acceleration in 3 subjects? If OTOH you had said you wouldn't accept subject acceleration, they would then have an easy option, just let her be in 2nd. I'd be inclined not to indicate to them that they might have that easy option, anyway.)
