I don't want her there.

I don't trust my friend and I have trust issues after a previous friend tried to steal my ex boyfriend. She did everything she could to get him and when it didn't work she was spiteful to me and said she was prettier, slimmer and more intelligent than me.
My current best friend who I have known for 3 years is beautiful to look at - blond and stunning but despite that is very unlucky with men. She makes me worry though.. she has admitted she would make a play for any man she liked even if married.
I feel very insecure becaue she has started wanting to come out with myself and my boyfriend a lot. I just feel really uneasy about it. How do I tell her nicely I don't want her there.