I don't really think she'll be defeated. But a well-run hard-negative campaign emerging next time she says something particularly stupid, preferably stupider than that McCarthyian quote, could do some damage.
Ed Tinklenberg didn't start getting millions of dollars until the final two weeks against Bachmann last time around, and he wasn't a particularly good candidate, and he didn't even spend most of that money.
It's not like less crazy incumbents in far more Republican districts haven't lost to Democrats in well-run campaigns. See: Sali, Bill
You said in 2012. By then it is unlikely to matter cause the Dem in the legislature will probably try to screw her over in redistricting. If you had said 2010 I would have agreed completely.