How to get rid of someone....?

My fianc� likes to be a photographer on his spare time...he found this "model" on line, she is 18 yrs old,she bought over 7 friends last week end to do a photoshoot with,but for some reason she has lached on to my fianc�, she is coming again this week end with two of the 7 ppl who came over last week end....and she talks business with my fianc� as well. We do have a 7 mth old baby the studio is in my basement I have told my fianc� my feelings towards this he has pushed me away from the situation so much I now have to leave my own home with my baby for 5 hrs on Saturday night. I would just like to stay home...how do I deal with this girl? And without my fianc� finding out?