Why do bad school days always have to happen when my husband is home and listening? We can have a hundred great days in a row, then he'll sit in on one lesson and it's pure hell. I feel like he must think that C isn't learning anything and I'm the worst teacher ever! I feel like I'm getting less and less homeschooling support from him because of it.

I'm not sure what to do about this. We've taken a lot more unschooling method this year, with a lot of free time and reading heavy (focusing on comprehension and fact recall after reading), and of course, math. I feel like he doesn't believe me when I tell him about successful days. I don't know how to show him everything she learned.
How do you get support? DH was only half supportive of homeschooling in the first place. He would rather seems kids to public school with "paid" teachers — even though I have my master's in teaching.
Re: Ug.
My DH was also reluctant when we started, but for other reasons. He was worried more about the social aspect and my kids' ability to play on sports teams. It just took a year or so of him seeing the kids interact with other children and finding outlets for sports and he was on board. I actually put DH in charge of some of the things he was worried about (like finding the athletic opportunities) and that made him happy. Perhaps the same thing would work with your DH.
To be honest, we're using board games as our curricula for a lot right now. The kids are loving it and are learning way more than they were when we spent our days at the dining room table.
But even worse, even if I did have to send her back to school, she'd STILL be failing math!