How do people with blended family cope? I have a 3 year old biological child and a 7 year old unofficial stepchild we currently are working on a child together.
My amazing mum treats both the kids the same same but my mil totally blanks my child, it’s as if my kid doesn’t exist. I’d cut all contact but my stepchild adores her x
Source

I would tell her or get your partner too that you treat all the children then same or doent treat them at all. they are all our family and no one is treated differently. like it or lump it. put the ball in her court