I just have to jump in here and defend Momoko, or at least share how I see her. She gives Manami tough love, but I think it's hard as a parent/guardian/established familiar person in someone's life to not be alarmed when someone is possibly being "scammed." You just don't know, and you want to err on the side of caution--at first. Don't forget that Manami was also keeping her meetings from Momoko a secret in the beginning
I also think Momoko telling Kawahara to dump Manami was certainly *not* about setting the stage for herself. I think she knew that Kawahara was not right for Manami, and she knows Manami well enough to know that she wouldn't go crazy and stalk him. It was her way of ending the two, sarcastically and smartly.
Another important part where she shows her support to Manami is when she is the first to call after their fight and tell Manami that the club might not be a safe place for Kaoru due to the club president's past, because she knows Manami is starting to care for Kaoru. She is still looking out for Manami after all that.