MIL and husbands ex

Am I petty or? My mother in law is best friends with one of my husbands ex and brings her to family events etc. Shes even to the point where if I have a party at my house she tries to invite her. She keeps trying to make me be okay with being around her but it makes me and my husband uncomfortable. I mentioned this to her and she said “since you said that I have to tell her you don’t want to be around her because she had sex with your husband” which isn’t what I said so I told her I’d drop it. But it’s been getting under my skin especially when she tries to bring her to my house. Family get togethers she wants her there then so be it but my own house I just cannot. She thinks I’m being immature/jealous but to me it’s a respect thing. I tried to like her so bad but she’s my husbands ex they weren’t even together but 3 months. Should I get over it or stand my ground? And yes my husbands talked to her but he gets the same answer as me.

Let me add this is his ex his mom had hoped he’d end up with forever.