Quoting JessieLeeAnne:" Everybody parents differently. ((shrug.))"
true, but in a situation where the parents are separated and they have to co-parent, they have to work as a team to raise the child together. Not have the mom treat her one way and tell her doing certain things is not okay, and the father just letting her to as she pleases and not disciplining her. It's causing more issues for OP since her LO is acting out now after being with the father.
Me and SO parent differently, but the bottom line comes down to that we have the same set of rules for LO, we just do it differently. He would never go against what I ask him to do with LO, and I would never go against what he asks of me and if we don't agree on the way another does something with him, we talk about it and fix it.