Seriously? --- Spoilers
I understand we, the viewers, need to suspend belief while watching movies. I get that they are not real and are just stories come to life on the screen, but, seriously...
Are we supposed to believe that a woman is so depressed and despondent over her husband moving in with a home-wrecker that she is totally okay with her son's new girlfriend totally taking over?
She doesn't just flail around the kitchen half naked but strikes up a conversation about the mom's break-up right then and there.
She has the nerve to show up soon after with luggage and announce to Henry's mom that she's living there.
She takes it upon herself to decide Henry's brother needs a girl in his life and then climbs into bed with him to help him get used to the idea of being around a girl.
Further, in her gesture of "good will" toward the brother, she has sex with him so he can get through his first time!
No loving mother on the PLANET is going to allow her sons to be hurt like that.