I think that we as mothers as a protective thing get caught up in that... 
you will not feel better after you see her face, that only shows you what she looks like on the outside. My son was 9 when my Ex got a new partner, he liked her. Then I met her and because of my yrs of reading people I saw more than him. My ex said I was upset over nothing that she was good to our son. Then one day she got ahold of a person that we were both friends with and set me up for use to talk one on one. Thats when a found out more about her then I really wanted to know. She is one of those poeple who has no morals,she preceeding to flirt with men in front of me,she even allowed one to touch her breast. Of course the next day I told the ex what I had seen and felt. His reply to the whole thing...HE MARRIED HER. We were all at war for a yr or better. She then started to treat my son bad when his dad was not around, which as you might guess just fueled the fire in me. Now things seem better...I dont fight her anymore...my ex is fully aware of how I feel about her and the whole thing...if she hurts him in anyway she will be visited by the police...no games here. I guess the whole story stems on this....educate your child...then trust them and their feels..reassure them that no matter what she tells you you will never be anger with her...and ask questions when she comes home. Healthy questions like did you have fun at daddys....what did you do with daddy this visit...as she tells about going to the park ask if grandma went to.....something simple...she will tell you if something that you should know about...when you ask if she had fun...you will know how the visit went. Some people may disagree with it but i did that...thats how if found out that in his dad's home he was seeing her hit his dad and dad hitting walls. That explained why his started to hit things in his anger. Now his visit dad via grandmas house mostly. 
You will met her someday for me it was too soon. 
Then i have a friend who would rather talk to her ex's new lady than to him. 
Me i think that it is between him and I. I do let her in on conversations now...but i always tell her that in the end it is up to me and his dad...but I am 4 yrs into this