I think this sort of behaviour is her way to try and meet a need. She wants attention - and she's getting lots of bad attention from the both of you right now - but she also probably feels quite insecure and uncertain about things. Reestablishing a sense of security in her relatinoship with you may be what she needs first and formost, so perhaps getting your DP to back off a bit might help.
Do you have time to read? PET literature might be helpful. There's also an easy book - How to talk so kids will listen adn listen so kids will talk. It's probably aimed at slightly older kids but you might find it helpful.