In mid January our roomate came back from a trip home and 2 days beforehand she let us know a friend would be staying with her til she gets on her feet. We were happy and had no issue with it as it was her room she would be staying in.
Fast forward 5 weeks and that friend is now working and still in the room. She is genuinely nice and she actually fits in perfectly with everyone in the house but when I asked our roommate if she could contribute to the rent, I got a definite no as it was her room and she could let whoever she wants stay in it. She said that we have all had guests over and they never paid. My mum for 3 weeks and my roommates dad and sister for 2.5 weeks both on holidays. 
I don't want to force her friend out but there has been little sign of her actively looking for a place and I don't think it's fair that she lives here free while everyone else pays. 

TLDR Roomates friend stays in her room for 5 weeks, nice person with job, but won't pay rent. 