Did you ever think that maybe she asks why you like her because for at least the past 4 months she could feel you change towards her when you say you started to lose interest? She may know she’s attractive but that’s not the same as knowing if or why their partner is attracted to them. You sound like you can’t stand her and would rather be with your male friends, so stop wasting her time and end it. You’re 19, not 12, you should be able to say “This isn’t working for me anymore”.