Failing as a single mum and daughter acting out

Since leaving my ex 2 months ago (not my daughters dad but his been in her life since she was 10 months) my daughters behavior has changed (she's 3). She's so much calmer because she isn't being bullied by his kids, she was always bitten and even chocked on occasions. She not on edge any more. It was awful. But when we left we didn't know it was going to be there last time we were to see them. They were picked up by there mum and then me and him got into an argument. We were always fighting he was always drunk and very angry and just awful, and I just thought that's it I need to actually leave this time and it has to be the last time I do. So we didn't get to say goodbye or anything.
There's been days where she has asked to see them and I tell her that we can't and she looses it. I explain to her that we don't see them any more but she just wants to.
She's started to take control of things because other things are way out of her control. She gets me to feed her her dinner the last 2 months. She tries and tells me what to do what to wear. Everything has to be her way. She's started to sleep with me. For example if I have my sunnies on in the car and she wants them off me she will tell me and if I don't listen she will have a tantrum to they are off. She's been hitting me. She bites at day care. But I'm wondering if that's copped behavior from my ex's son.
Now we are moving interest in a months to live with my mum because we don't have any family where we are. Shes going to have to say goodbye to her friends and her day care. My dad is about an hour and a half away he moved about 8 months ago away from us, so she isn't going to see him like she does every so often. I'm so worried about her. All this change is happening in her life. We are packing up the house now and she keeps saying we are moving to Grandmas. She seems excited. She's close to my mum and my sister along with the extended family too so I'm hoping that's enough for her. She will be going to a new day care at the start of next year which is going to be huge for her.
We see a counsellor as I had PND when she was born and I've never really known how to interact with her properly. She's been good and is talking me though things but I still feel lost.
This is a huge move for me as we moved here when she was 3 months. So I'm going to miss my friends and everything. So it's huge for her too.
Shes never meet her dad either due to DV he didn't want her never asked to see her, so that's another thing in her life she's going to have to learn about when she's older.
Has any one been in this sort of situation? Is there anything I can do?
I really don't want to her to have any trauma or anything that's going to effect her when she's older or even now.
I feel so guilty like I've totally ruined her life already. Sometimes I think I should of stayed with her dad but I know if I did I would of lost the pregnancy for sure. Then I blame my self for getting into another DV relationship. And not seeing the signs to it was will with in a year. I feel I've screwed up enough. And I'm scared of moving back in with my mum I will do something else again and screw up.
I'm so lost. I'm so worried about my Little girl.