I was going to start this post by promising that I wouldn't mention potty training again - but honestly, I'm lying. I will mention it again because I have very little else going on. After some reflection, B and I decided not to treat the no #2s in the potty thing as not a thing. She continued to hold off until she had a diaper on (usually at night, sometimes in the morning just as she was waking up), and we'd continue to tell her: Next time, it's in the potty, OK? We'd put it where it belonged (in the toilet), flush it down, and that was it. After making the decision not to treat it as a problem, I found it a lot easier not to get upset or frustrated that she wasn't responding.
I did, however, search the library for some potty training books, just to have a bit more of a reference on the topic than just google. But! This weekend! Mia requested we go to the potty because she had go #2. B went with her - maybe a change of pace on who was with her would make her less nervous about it all. And sure enough, she went, and boy did we celebrate it. She was a bit surprised at how happy it made us, I think, but she was very proud of herself. While we aren't quite at the point where she's going in the pot every time, it's been a huge sigh of relief that she's at least willing to try. She's told us every time she's gone, and sometimes we make it, and sometimes we don't, but... we're getting there. So... YAY. I'll still waiting on the potty training book to be transferred from a different library - maybe we'll have a bit more insight to share on this problem once we implement whatever they recommend.