They responded that it was fine, and then it was posted a week later, without informing me that she'd found another beta.

That's so rude. *sigh* Plus, you know that if the beta job didn't take very long, it probably wasn't good.deep.

it might be worthwhile to check over the fic and see if you can clean it up a little

I definitely think that's a writer's responsibility. Having a willing beta shouldn't be used as an excuse to write poorly in the first place.