Whenever I see my mother-in-law doing something with my toddler that makes me uncomfortable and ask her stop, she ignores me and keeps doing it. How do I get her to respect my boundaries?

Today my MIL let my 16-month-old crawl up to her in-ground pool and lean over to touch the water, while she held her up by the back of her shirt. I immediately became extremely uncomfortable and it showed. I was terrified, actually. My daughter does not know how to swim at all. When I said that I wasn't comfortable with this or with my toddler crawling around the pool area by herself, she blatantly ignored me and let her continue dangling over the edge of the pool. I had to ask (more like urge) about 4 times before she picked my daughter up and moved her away. She did not apologize or acknowledge the boundary I tried to set.This happens all the time. If she decides she wants to do something with or for my child, she does it and does not ask myself or my husband if we are okay with it, and if we ask her not to do something she blatantly disregards our request and does it anyway. She really means well and I love her dearly, but I don't know how I can make it clear that I am the parent and I have boundaries that I need her to respect. She does these things to be a loving grandmother but there are just some things I don't agree with and I don't know how to get through to her.EDIT: I normally would have just gone over and picked up my daughter myself, but I am almost 8 months pregnant and could not physically do so without being at risk of slipping while trying to pick her up. I didn't think that would be a safe solution for anyone at the time. via /r/Parenting http://bit.ly/2PAvxIi