Like I said, that already happened. When Monica first joined the Avengers, Scarlet Witch was on the team way back when. She-Hulk was there, too, and Jan rejoined the team, somewhat later. You'd think Monica would have a more lasting connection with one of the three.
As for Carol, if you pressed her about it, she'd say that she had more of a right to the mantle; Monica was just casually borrowing the name. Hardly a shared thing. I mean that is why Carol took the name, right, without first letting Monica know as a friendly courtesy, if nothing else? There's really no reason for Monica and Carol to be BFFs due to the mantle. If anything, that little bit of shadiness from Carol would be reason enough for Monica not to really trust her that deeply now that she knows how Carol moves. Monica will always be the bigger person, but don't mistake that for her being a fool.