I mean, it would probably be nice of Peter to tell her that a younger, alternate, version of her best friend is currently stuck in their universe so she doesn't just stumble into her...although he might've had other things on her mind and timeline-wise maybe MJ was gone when Gwen showed up in 616 on a more permanent basis?
That makes me think...physically Earth-65 Gwen isn't an exact match to 616 Gwen (although that sometimes depend on the artist) but does she have the same voice? But I guess that's probably muffled under the mask.