How do I tell my coworker I don't want to be friends

I have this coworker who I went to hang out with outside of work once and is was fine but then I found out how badly she talks about the kitchen staff. I work at a very small hospital and she talks about the kitchen staff so poorly. She constantly says how she knows they're broke. Living in their section 8 houses that probably have roaches. She doesn't know a majority of them so idk how she knows they're broke. All of them are people of color so I'm not sure if racism places apart in it but even if it doesn't I just don't like her attitude because most of them are so sweet. During lunch one guy was asking about picking up more hours to someone and she talks about how his electricity is probably cut off in his section 8 houses. I asked how she knows that any of them are on section 8 and she said she can tell. Work had a pot lock and she was saying how she's not eating any food brought from any kitchen staff house because it's probably a roach infested nasty house. She has been trying to hang out outside of work more and I just don't want all the negativity. I don't want to be friends but still want to be civil at work.