Dealing with bossy, bitchy room mates?

Help! I just moved in with my boyfriend and he shares a house with his brother and his girlfriend. It's been two months and I am very happy to say that my bf and I are doing great. As for the other two, not so much. The girlfriend constantly complains that about things not being clean enough. Keep in mind that no one in the house is a real pig, we just all work full time (except for her) and sometimes dishes don't get done the very second their done. I am not a slob and this chick doesn't need to be harping over my bf and I to clean. How do I tell this ***** that she isn't my mom with out putting a wedge between the brothers?