How to handle my husbands Ex...

I've known my husband for over 8 years. We've been married since June 2015. During his Jr. Of high school there was a chance he got his girlfriend pregnant during there Jr year. However they broke up and she didn't even tell him about the baby til the day she was born. The summer after she had the baby she got married to another guy and he is who the little girl calls daddy.....there has never been DNA testing to prove she is my husbands child... Fast forward til present day... About 3 months before our wedding his ex randomly started sending him photos of the lil girl who is now 4 and her new child. Kinda as a way to stir up trouble. My husband asked her to quit. Then a few months after our wedding she did it again and he asked her to quit. Then at the end of December my sister and I was walking into a store and happened to pass her and her new husband whom she just married. The next day I received a message of Facebook from her husband stating to let my husband know his child is taken care of etc. I simple told him we have no problem going thru the courts to obtain visitation etc.. well today I walked into another store and she happened to be working. I simply bought what I needed to and left. About 15 mins later I got a phone call from my husband asking about it because she texted him. I really want to call her out and tell her how it is but I don't want to go against my husband. He chose not to do anything about finding out if the little girl is his and I support him. But I refuse to have to live on egg shells because of the chance of the possibility of seeing her in public. I've never even spoke to the lady before... how do I go about dealing with this?