Yeah, it probably was an asshole move, but to be fair, we have no idea what really went down at dinner that day. LW's narration has so many gaping holes in it that my guess is that, in an effort to protect herself from unwarranted parental wrath, she duly threw Lisa under the bus.

Which didn't work, hence the grounding, but I can understand why Lisa would be so pissed off she'd be talking about it months later.