Yeah, the BF could still be sketchy? But if not-Sara isn't interested in dumping him for the name thing, it's not like LW can do anything about that.

And if LW is worried about their daughter accepting crappy behavior from boyfriends, which IS unfortunately a thing young women are heavily socialized to do, then I think a stance of "Remember you have a right to draw your boundaries wherever you want and defend them! I support you!" is way more likely to be helpful than "You're putting your boundaries in the wrong place! Listen to me, not your boyfriend!"