Diary of a Mad Fat Girl
Diary of a Mad Fat Girl is the story of Graciela "Ace" Jones. Ace is in fact a fat girl (although the descriptions of her in the book sound more like chubby) who has a lot to be mad about - she recently broke up with her fiance, her friend dumped her right before a planned vacation, another friend is being abused by her husband, and she hates the principal at her school (she's an art teacher).
The main plot of the book is dealing with the abusive husband situation, although there are plenty of subplots. I was surpsied to learn that the book is not part of a series, since that's certainly how it reads (per the InterWebs, it's apparently a super-popular self-published e-book that was later made into a dead-tree version). There's nothing that happens in the last 20 pages that you don't predict in the first 10, but it's a good ride. Ace and her friends are funny, and the misadventures are wacky without being over-the-top. Then, of course, the good and bad guys get what they deserve and everyone lives happily ever after.
Does it pass the Bechdel test: Yes. Ace and her friends spend A LOT of time talking about men, but they do also discuss other things - fat, work, money, and Ace's chiweenie, Buster Loo.