Remarks by MIL

I’ve been taking care of my child full time since birth, and MIL keep thanking me for taking care of my own child. I feel annoyed when I hear that cause it’s not like I’m a nanny taking care of her grandchild? I’m the mother, why does she need to constantly thank me? Context: When i was out from confinement and the in laws came to visit baby, MIL said to me ‘baby X is our Lee zai zai you know?’ It’s as though she’s telling me my baby is their family’s baby? I still feel so disturbed and angry whenever I think about that comment or listening to her thanking me 😫