Faye is honest. She stands up to defend her friends (witness the whole Vespa Avenger thing, her run in with Sven after he gets Marten involved in his nonsense). She's smart, she's funny, and when you want to have a full on snark fest, she's the best. She will play along, and when she's wrong -- usually -- she apologizes. Those are pretty big qualities.
It's reasonably apparent in the archives. Yes, Faye is the 'Troubled Friend', but, damn, if you can only see her physical assets, you aren't looking. If A is friends with B only because of great tits, etc,. then A is capable of greater assitude than Sven ever imagined.
As for the 'she's written to have friends' thing -- true, but shallow. If the friendships in the writing didn't make sense, few folks would be reading this, much less discussing it in a forum. The writing has to have a consistent interior logic or it would just be so much garbage with pretty color illustrations. It wouldn't even engender the question of "Why are people friends with Faye"?