The story so far...
Met DP 6 months ago, we are moving in together to a new town this weekend. He has been very involved with my DDs (5 and 4) from the start, and has been fantastic. He has helped me with raising their standards of behaviour, disciplined them with me (after we had discussed it and agreed on how we would do it) and has been affectionate and loving with them, all of which I am happy with. He has a DD of his own (3) who he has every other weekend, who is lovely and well behaved, both me and my DDs get on really well with her too. All good so far.
Over the last few weeks we have had DP DD most weekends and went on holiday together. DD1 has started acting up and it is clear that she is jealous of DP DD when she comes to stay. DP doesn't treat my girls any differently to his own DD, and we are running out of ideas as to how to deal with her. She keeps on trying to get both DP DD and DD2 into trouble, backchatting, attention seeking etc etc.
I appreciate there are a lot of changes for her to deal with, but I really don't know how to deal with her behaviour, so far we have tried to come down quite firmly on the bad behaviour and azccentuate the good, but it doesn't seem to be working, please help.