[This is more commenting on the options you've got than offering new ones, sorry; I realise it's not what you asked for.]
Why do you say homeschool for a year? Just in order not to look beyond next year, or do you think middle school is going to be much better for her? (That doesn't seem to be what people say in general about US middle schools, but ymmv!) I think you may need to be looking a little beyond this year, just in terms of: is middle school something you think will give her things she needs, or something to be got through as fast as possible...
To clarify: to skip 5th entirely, and go to middle school in a few weeks, she'd need to learn the US history content of 5th in the next few weeks, is that right? Is that the only thing you're doubtful about her passing in the tests for skipping? How does she (and how does your DW) feel about that option?
Can she take both the tests that would let her subject accelerate to 6th in maths and the ones that would let her go to 7th, or do you have to commit to having her take one or the other (so that just missing the cutoff for 7th would leave her in 5th grade maths? or would they do the sane thing and put her in 6th in that case? how would it work?) Are you basing your estimation that she could go to 6th but is borderline for 7th on a careful look at the syllabuses? I don't know how it is in your state but I think this is the stage where there starts to be a fair amount of Stuff in US maths classes, i.e. it'll be more important than it was with her earlier skip to make sure she's been exposed to everything she needs.
If she doesn't full skip this year, do you think she will probably be doing it next year (skipping 6th)? One option would be (with or without subject acceleration for next year) to spend next year planning for her to full grade accelerate next summer, i.e. over the year she's in 5th, afterschool whatever's in 6th that she doesn't know now. Of course that leaves you in a fix if you decide not to go for a full skip next summer, or she doesn't get it - it leaves her in 6th learning a bunch of stuff she's already done in afterschooling. Hmm...
On the subject acceleration side, I don't think it would make much sense to subject accelerate her in science without also doing so in maths. At least in principle there comes a point where the science needs the maths anyway, so getting science ahead of maths formally requires a way to undo that later. And it's pretty clear (isn't it?) that one year of subject acceleration in maths is within her capabilities anyway.
I know I'm like a scratched record on this (that simile's not going to last, is it?!), but what are you doing for her problem-solving abilities in maths? Manipulating fractions is all very well, but it ain't maths :-) Don't let her off doing the fun stuff because she "isn't intuitively mathy"! How does she do if you give her
a JMC paper for example?
