The only reason I can think of that she'd do that is she has a D that is a few years older than D3. I think in the past she's tried to get my ex to bring D3 over to play but my ex has just blown her off...which is kinda sad given that D3 has fun playing with her D.
It's also kinda weird that I'm on as good if not better terms with my ex's mom and sisters than my ex. I've frequently promoted contact between D3 and them, whereas my ex hasnt promoted contact between D3 and my family at all. I came to recently understand that such things are given consideration in a custody hearing...which parent is more likely to promote a R between the child and their other parent/family.
Something else I just noticed was in my signature, I have the date of the night I went over to her dads house and caught them together. It hasnt even been a month since that happened...so its not like my ex will have months of texts and emails...more like a few weeks. Not that they wont be damning...but 3 weeks of contact/begging/reasoning/etc. in an attempt to reunite my family isnt the same as 6 months worth. So while its not great...now that all non-D3 tlak has been cut off...its not as bad as it could be.
In a way my ex filing for custody might have done me a favor in the sense of limiting her ammo.