My sister friend wants to “Cuddle”

So my sister has been planning a trip to see me and she’s paying her friend to drive her out here to see me. She is 18 years old and this friend is a guy I’ve never met. She says that he’s just driving her out here and then staying with her and sharing a bed. I get that my sister is 18 and she can make her own decisions legally but I don’t know about this one. She says her friend just wants to cuddle and he’s not that kind of guy but I think it’s weird. If I let her stay with me she will be most likely sharing the living room with him but if I don’t let her stay here I won’t see her at all during the trip. What do I do?