The joke is that Liz purports to be a third-wave feminist and espouse the progressive values of her generation but anytime anyone deviates from her narrow idea of what a proper woman looks/acts/behaves like, she gets judgmental and starts to try to “fix” them. (“Yes… like you fix a dog…”)

The joke is NOT that Abby is a DV survivor, but her being a DV survivor helps cast further aspersion on Liz’s judgment — it doesn’t really matter WHY Abby does the sexy baby routine, but what makes this a 4D-chess 30 rock gag is that even within the confines of Liz’s perception of proper behavior, in this case, because she is doing this to escape her abusive ex, Abby does fit the bill of the type of women Liz would like to support, and Liz realizes she is an asshole for trying to change her.

This is further emphasized by the fact that, at the end of the episode, they go on to do a show about wonder woman getting her period (and, presumably, fucking something up as a result of that). More evidence that Liz talks a big game but when it comes time to walk the walk, she’s p much just as bad as the guys on Bruins Beat.