Welcome Success!
Yep! 156 is her IQ, and (assuming they didn't do extentended scoring) and that on a test that is designed to go to 160 as a maximum. The IQ numbers don't really measure 'how smart is the kid' it's more, how unusual is it for a child to be able to answer the questions she can answer. In your case it's really unusual. This should set your mind at ease about the schools - it's not that they are doing anything terribly wrong, it's that your daughter has learning needs that they just don't run into very often. Or ever.
You might remember scores like 170 or 220 from 15 years ago, but there has been a big push to get rid of those sorts of numbers in the 'modern tests.'
My advice:
1) Apply to Davidson Young Scholar Program
2) Read '5 levels of Giftedness' by Deb Ruf
3) Read through some of the posts here
4) Read through Hoagiesgifted.org
5) Join your state gifted association
6) Post here about what you've read and what you think of it, what you've tried to do to help your daughter and how that went, and what you think she might like to learn.
7) Seriously consider homeschooling.
Love and More Love,
Grinity