What to do with exW?

[BuildingBlocks9]

I have been with my DP for the almost 2 years and I have recently given birth to our DD. DP has a DD (almost 3) from his previous marriage – the relationship broke down when his DD was 1,he moved and divorce was granted in Jan 2015.I met his DD in Feb this year (taking her to restaurant and park couple of times).He has not told his exW about having a new partner and a baby (told her 4 days before birth).She is a very argumentative woman and we were worried that it may impact on my pregnancy and new baby.Now she is taking him to court that at the last hearing for custody (back in Feb 2015) he had not revealed the info about new partner nor my pregnancy, that he had not disclosed it and the shared residency order should be cancelled.We knew that once she know about me and our DD she might flip out. For the sake of his DD he lives in a rented accommodation (as he has EOW and couple of overnights per week), in a years time we are thinking about living together full time (moving to a larger place that his DD has her own bedroom). He brings his DD to spend time with us, we organise outings as a family,we understand that she needs to accept me and her DB slowly.
How can I help my DP? Shall I get involved or take step back?

[wannabestressfree]

You still haven't met her? Shame on you...