Quoting
llworking
I am not talking about Parent B demanding that the stepparent have nothing to do with the child without Parent B's permission. I am talking about the stepparent having enough respect and courtesy to NOT do certain things without making sure that both parents are on board with it. In the first scenario Parent B is being overly controlling. In the second scenario the stepparent is directly causing better co-parenting by voluntarily showing respect and courtesy.
I will give a prime example from my own life. When my daughter was 12 my ex's girlfriend (who worked in a hair salon) colored my daughter's hair after I had expressly told my daughter that she couldn't dye her hair. I felt that she was too young to start that cycle. When I expressed my displeasure to my ex, his girlfriend seriously apologized to me and stated she would never have done it if she knew I had said no. Her apology set a tone between her and I of mutual respect. It would have been better if she had checked with me first, but the apology made up for it.