Either way, that’s all outside the scope of this AITA.

It is all part of the discussion, and I think relevant information to analyzing the situation and potentially helps explain why the daughter acted the way she did. Even with that, though, I did not give judgment here, so it wasn't really the point of my comment. I was simply replying to you assuming OP would have cooked for Megan and saying that is not really a fair assumption given all OP has said. OP asked if Megan was coming, but has made no mention of how she would have planned to make her something IF she had known. In fact, OP has not answered that question anywhere I've seen someone ask. She has only repeated that she does has never cooked for Megan in over 2 years of dating Megan's father despite them spending lots of time together. That means even when Megan was 13, 14, and dependent on being fed by her family, OP did not provide for her, which seems really suspicious .

Does it change whether she is an A for not having something now? No, because she didn't know Megan was coming. But it is still valid information for people to want to know as it could explain why the daughter reacted the way she did.