I LOVE this pairing so while i was watching that episode i was thinking " why cant they use that same flame shield spell on finn that was used on jake in the episode where flame princess was introduced. then they could actually kiss or hug! sometimes the writers dont think!
Well, I think that Flame Princess could be not fully a fire elemental. When she got wet in the rain, instead of her hair going out like fire would, it just behaved like normal hair. Maybe she could be stabilized enough so she wouldn't hurt Finn.