It sounds like she's a hikikomori. I would recommend looking into that that is, they don't only exist in Japan. There are articles and videos about it.
A lot of these people tend to be very shy and anxious. There house is usually a mess. And sometimes they have a hobby that helps them cope, usually being something like video games or anime.
I met some shut in here in the US. I also notice when they do make friends, they get too scared to invite them over because their house is a mess. You could use that for a plot to a story.