Based on what you offered as an example, I wouldn't assume she (or anyone else who doesn't/can't have children) "hates". I think it's natural for someone to enjoy being with a child/children; but one problem can be that the person who doesn't have/can't have a child doesn't know how it is/feels for someone else who has children. Missing the "full depth" of how a mother feels toward her child (assuming the mother has the "normal" thing of maternal instinct/bond; the person who has no children can often tend to see all children through an "all children" lens. OR, the may really love a friend or family members child but not realize that their love is still no the same/equal as what the child's mother feels (again assuming the mother and her child have a normal bond).
As far as "thinking she should be able to over-rule" goes, it can be tricky to think one knows what someone else is thinking; BUT, if she really thinks that way that's a whole other thing from what I said above. That's just out of line of her. Sometimes people do that if they think they know better than the child's mother (maybe they do, maybe they don't), but believing one has, or should have, some right to "over-rule" the mother of a child/children is just out of line.
To me, the only time someone else might have a legitimate reason to "expect to over-rule" the mother of a child/children might be in the case of kids and their mother being in someone else's home, the kids acting up and making messes/risking breaking things (or even hurting pets or other guests); and the childless person expecting the kids' mother do something about her own child/children.
Sometimes if/when there seems to be "hate" vibes coming from the mother who lets her child/kids run wild aren't about the fact that she rightfully expects to be her own child's mother, but because she thinks her kids should be allowed to run as wild or big as big of jerks as they want to be in the home of someone who doesn't have children.
Similarly, if the mother has well behaved and happy children the person with no child of her own may think the children "were just born that way, and the mother of them is 'just lucky' to have such great kids". "Just lucky" thinking and/or lack of awareness of what it takes to have nice kids can be what a mother resents/won't have from someone else. That can be seen by the person prone to over-stepping/not recognizing different relationships) bounds as an "insult" of someone who means well.