To me, it sounds like your mom had some expectation of how the grandmother-mother-grandson relationship would be and reality isn't meeting that expectation.
It's ok to tell your Mom how you feel. Honestly, it's good to have that open conversation in my opinion. Because if you don't then those feelings fester and end up popping up later, usually worse than if you just brought them up in the beginning.
Being a grandma doesn't mean that you are the expert, you get to tell everyone everything you think, and the parents will then do exactly what you say. To me, your Mom isn't respecting you as a parent. I'd sit down with your Mom and ask her what she means by "not respecting her as a grandparent". If it's about you doing things her way, let her know what you want to use her as a resource, but that it is important for you to find your own parenting groove. So you need some space to try things your way and you hope she can give you support when you have questions or concerns. Then, I would sometimes (even if you really don't want it) ask for Mom's advice and take it. Let her feel involved and important.