Since you filed for divorce isn't there something legal indicating how much time you get with your child? You shouldn't be trying to settle this directly with her, but going through your lawyer.
It's pretty typical for spouses to do this type of thing with the kids. Generally they do it to make a spouse angry or hurt them. There is a chance that if you did the opposite (didn't get angry and just backed away, or offered to watch child as a "favor" to her so she could go out and have some time for herself) she might change her reaction. It's just an idea....
Also, document this. Document EVERYTHING for court.
It doesn't surprise me she's angry at you for telling her family she's out "partying." If you are divorcing her the relationship she has with her family is no longer your concern. Also, it's tattling. The only thing you should be doing with this information is logging dates and times of this type of thing into a journal and saving it for the court to indicate why you should receive more custody.
If anything you should want her out partying because this will look bad in court and help insure a good amount of custody. Maybe even get photos if possible! Heck, encourage this bad behavior, the worse she acts the worse she'll look in court.
There is no arriving, ever. It is all a continual becoming.
