She’s feeling it. I don’t think it has to do with you, but when a mother feels somewhat “threatened” in their role or someone else tries to mother their children, it’s a tough pill to swallow at first. So she probably hates it, is dealing with it, but knows there isn’t anything she can do about because she knows her kids are fine.

It really stinks as a mother. It’s the hardest part of the divorce whether it was her decision to divorce or not.
Give her some space, it will blow over