This. I also like how it contrasted with Amy's more childlike "I know Dad is mad, so I should say sorry, though I don't really get how it's my fault" apology.* Once Liz got the fact that it was her fault, whether she remembered it or not, she owned it. And even though she did a horrible thing, you could come out of the episode knowing she'll do better because she recognizes it.

*No disrespect meant to Amy, of course. How she (doesn't) handle emotions is one of my favorite things about her.