Boundaries/Pregnancy Myths/Controlling Family

So I'm 25. I'm staying with my 70-ish year old aunt for the remaining 50 some days of my pregnancy - several states away from home, to get wayyy better healthcare. I understand when some people get a little overprotective and a little bossy about things while I'm pregnant, it's only because they care. I'd like to think I'm pretty good at setting boundaries. But, not with my aunt. She isn't just a little overprotective. She knows everything and you can't tell her otherwise. All those old wives tales? Oh yea, she strongly believes them and cannot be convinced otherwise. Sooo, I mentioned buying myself a bikini and going to the pool sometime soon. Oh hell. Bad idea. She didn't suggest, she didn't express worry, no, she straight up commanded I not go in a pool because I'm pregnant and it will hurt me and my baby. The pool is next door, it belongs to my other aunt. I would feel absolutely stupid to sneak around to swim, because I'm an adult capable of making my own decisions and should not have to explain myself, shouldn't have to explain why my actions are okay or even encouraged by doctors, shouldn't have to explain anything. Seriously, I don't know how to deal with this, and her commanding I use the hospital she decided on for me (yes, she has told me what hospital I will be going to for prenatal care, which I did let go because she does know the area better than me and also it seemed more convenient and closer than where I originally planned 😑), and other things. I don't want to rock the boat so I'm trying hard to pick my battles. It's a little too much with her though. She is very bossy and I'm not used to this. Please help me, examples of boundaries I can set without being hateful or seeming rebellious or defiant to her, because that would probably piss her off. Like seriously, I don't think my ego is hurt as much as I just feel like she commands things and steps over my boundaries. I just think that 2 adults should not be bossing each other around about stuff like that. Or, one adult bossing another around. I felt so small when she did that.