should my girlfriends 23 yr. old daughter be allowed to have guys stay overnight in my house.

when i first moved in with my girlfriend, it was her apartment. she allowed her daughter then17 to have boys stay overnight . now we bought a house together, her daughter is now 23 and pays no rent. i have laid down the law and said she cannot have overnight guest. she said we let her before why can't she do it now. i said because this is my house. whose right