Imma be honest, dunno why everyone in the comments is losing it at her and calling her a bitch. This is pretty standard stuff for women. They have a much higher veto power in their friendships in terms of which guy their friend dates, because a girl generally highly values the opinion of their girlfriends when it comes to the guy she likes (unlike men). It's called social proofing or preselection, it's to make sure the she isn't investing herself in a guy who other girls think is a loser. Girls pay a much higher cost to picking the wrong mate (risk of pregnancy, increased risk of STIs, being more physically vulnerable than guys, etc), so they vet their partners much more strictly than guys do, especially at the initial stages of dating.
From her POV, this guy IS objectively an absolute loser. Let's be honest about the type of story this is - wish fulfillment of a plain loser boy being liked by the "idol" of the class. He has no social status, other people in his class avoid him, and all of his interests are nerdy or weeby. IRL, he would be treated like a loser, of course we know he's a good man at heart and we like him because this story is told from his POV, but that's just not how we judge people in terms of status IRL. She thinks that a girl as beautiful as her, with a much higher mate value than what she currently bargains for concerning this "loser," she thinks her friend is doing herself dirty, which is why her exact words were something like "You need to have a higher opinion of yourself." All of this is because she's grateful that she stood up for her when no one was watching when other girls were shit talking her (primary form of aggression for women to use on each other - reputation destruction or social ostracization, - this is how girls bully others since they don't have the physical strength that guys do.
Of course, she doesn't know that the reason why she likes him is because he called out to her before when no one else did, back when she was a loner herself, not too unlike what her friend herself experienced, and why she likes her so much. Maybe once she knows that about him, she might come to approve of him as a suitable guy for her friend.