I remember really liking Serina when watching the anime. She's the one that clicked for me most readily among Anna's friend group. She's very protective and very serious about it, but I admit that sometimes she can be overzealous, but I appreciate that.
Her reaction to Kyo was most likely an impression that he was mocking them, for whatever reason, and considering they don't know each other very well, it's not an entirely unreasonable reaction.
Give them time- Kyo has to find his place among Anna's friends, then the whole gang can hang together.