Nothing wrong with being selfish.

The idea and fear of being called selfish just seems like unneeded pressure from yourself and others who use that label to pressure you into something that could ultimately make you feel spite for your friend, and regret at yourself for having let it happen, possibly causing a fissure in your relationship.

Not any less of a person for trying to preserve your relationship. Doesn't make you look bad for doing so while others tend to expect you have 100% trust in everyone or else you're a bad person.

Your friend needs to find out something else for her living arrangements.