MIL keeps playing favorites with my kids

When I had my son (3y), my MIL was thrilled. She wanted to be a part of everything, including going so far as to try to design his nursery (in a completely different theme than I wanted) and she picked out his first Halloween costume (despite that we had already purchased one). Lots of boundary issues, continuously crossed because she wanted to be so involved.

Well it’s been a completely different story with my daughter, but not in a good way. My MIL has watched her once since she’s been born (1.5y) whereas she will get snappy with us if she goes more than two weeks without seeing my son. When my MIL runs errands, she continuously picks up gifts, clothes, and treats for my son, but not my daughter. She makes excuses saying that there’s no cute girl items and etc but even when they just got back from an out of state trip, she brought my son a souvenir but not my daughter. I truly don’t understand why she would be playing favorites with our kids and I’m not quite sure how to address it. My husband recognizes it, but just kind of rolls his eyes at his mom and says “yeah I know “ but doesn’t address it.

Is it ok for grandparents to obviously play favorites?

I don’t like when people play favorites. My dad favored my step siblings over me & I haven’t talked to him in a few years because of it. I would tell her straight up that she needs to either buy things for them BOTH or don’t get either of them anything. She’s little now, but she will grow up and see what’s going on. It’ll hurt, she’ll resent, & it’ll just go from there. I would nip in the butt now.