Don't expect her to take responsibility for her own failings. I mean, of course she ought to, but she doesn't sound honest enough for that. She sounds like the type who'd blame you for something that isn't your fault.
Anyway, if she's not going to look out for you, you need to look out for yourself. Don't let yourself get in a bad way because of her negligence. Also, as someone who did something similar once: if you let trash cover your floor, bugs will show up. (I don't know about you, but I hate bugs.)
Is there any way you can arrange things so that the trash can can't be knocked over? Like, put it against a wall and place some big things around it, or use tape to secure it? I think there are also youtube videos about keeping dogs from messing with trash, but I've never lived with a dog, so I don't really know what'd work.