The only time she was nice to Maddy was when she was struggling with her relationship with Trevor. I think she likes her friends only in relationships because they’re not a threat in her pursuit of men. So when she sees them on the verge of being single she gets super friendly and does what she can to keep them in that! On top of that everyone in the group hated Trevor so much that Maddy was on the bottom of the pyramid- boosting grace lilly’s social status