Although people say it’ weird because they’ve only met each other for a short amount of time, I believe the real issue is her personality. If she had a more outgoing and active personality, her hanging out with someone she just met wouldn’t feel so strange. And although you’re trying to make it feel as though they get along well, in the future try creating a sense of mystery about the girl. It doesn’t have to be to be a crazy or sad backstory, we just need to get a sense that we don’t fully know who she is yet. People don’ expose all of themselves to strangers and we the audience and even the mc need to feel that.