Thanks for the support, everyone.
Finally got my landlady to sign something officially terminating the lease. She was reluctant to do so, saying that she thought we were "friends", or something. Uh, yeah, I'm not stupid enough to buy that line. She was also hugely ticked that I phoned the city about the kitchen leak. She's a lot craftier than she lets on.
Chalmette, thanks for the medical and legal advice. I'll probably go see a doctor only after I've moved out, since I'll finally be free of this bad air. As for my last month's rent, she was clearly unwilling to give it back to me, which is unfortunate for her, because now I'm really in the mood to stick it to these people.
I'll tread lightly, making sure my lease if in fact officially broken, but I think I'll now make sure the other tenants of this house know about the mould problem (which she denied, by the way, even after I showed her the pictures I took). One of them has a child, so it's probably the right thing to do anyway.
Also, my heart goes out to all those people who had to deal with such issues along the Gulf coast. I was reading a lot of stories on-line while I was researching this issue, and it just sounds awful what a lot of people went through. You have my sympathies.