Right or wrong

So I live in a house with 7 people and 6 dogs. My girlfriend and I (both 21 years old) both work and go to school. Her parents and her brother (24years old) work. And her little sister is only 15 therefore she goes to school. However my girlfriends brothers girlfriend (21 years old) lives in the house... doesn’t work and doesn’t go to school or contribute financially to the house what so ever. Is it right that we expect her to do most of the house work with us contributing when we can or should she not have to contribute at all. This has been an argument between members of the house especially since my girlfriend and I are super busy and have a lot on our plate. Thanks for your input