Her own brother was chauvinistic to her times because in that time from all the writers, artists, and other creatives were male and this was before the women’s movement.
And in real life even if you were mean to someone decades ago does not mean you can’t be hurt by their loss.
Mastermind himself was an abused, but he was an abuse victim too. Dominated by Magneto, he wasn’t a particularly attractive guy. He certainly did abuse his illusion powers but given the context it’s not hard to say why.
I think people might try concepts like empathy and forgiveness before holding grudges over something 58 years ago.
Notice her brother drank with Mastermind and his other colleagues. They were all sad at what happened. Probably because they all got second chances on Krakoa, while this happens to Wanda.