i know how you feel.
its like, they already raised kid(s) so they feel like they know better right? and you are just a "beginner" - you must not know what you are talking about. they way they do things is just fine.
i dont know. maybe limit the time she goes over there or something. or, figure out which one of these complaints you have the biggest issue with; for me it would be the swimming. lie to them if you have to. tell them shes going to/is taking swimming lessons and the instructor knows shes got some fears with water (no doubt due to their PUSHING her into it) and that he/she instructs that she NOT be taken to the pool. if possible, get her into some lessons WITH YOU or her dad, so that she can learn about swimming, and not have to deal with being pushed into it with gma and gpa.
you might have to remind them that anything they do is going to reflect on them in her mind. shes obviously going to remember continuously being pushed into the pool, and the fear and stress about it. and shes going to connect that to them; making her fear and stress about being with them. if they want her to look forward to being with them, and if they want her to be happy around them, they have to stop doing things that are causing these fearful mental impressions.
another thought; maybe shes having nightmares about the pool? you would rather not be awake for an hour in the middle of the night over a nightmare.
lol. i must be a horrible person suggesting you lie.
i get so frustrated too; my ILs did the same kind of thing with my son. hes finally to the age where i dont have that many worries really, but they still do things like letting him out in the sun too much and stuff. its frustrating; i mean, we get scared because they say all it takes now is one blistering sunburn and skin cancer is in the future. thats horrifying! its like, cant you understand that i want to protect my kid?
chances are, if the sunburn is in spots, they are just not sunscreening her properly. tell them NOT to skimp on the amount, when applying her skin should be white from the sunscreen, and yes, rub it in. this isnt a lotion that you just barely get the skin moist; you have to use quite a bit!
hopefully your husband will back you up; at the very least he will sit with you on your side and at least acknowledge your feelings in front of them. this isnt the time for him to defend their "rights" as grandparents or as his parents. this is the time for him to understand and agree with your concerns; its not like you are requiring a 12 course meal while shes there, you just want to keep her safe, healthy, happy and avoid the huge water fears that most kids have naturally.... and keep it from turning into something debilitating. this could affect her whole life; a fear of water turns into a lot of problems down the road. i mean, water/swimming is a very "important" thing in a kid's life! whats more fun than swimming on a hot summer day? LOL
anyway, you really need to have the conversation, taking it one topic at a time. just ask them if theres a reason that things are happening. tell them your concerns, why you want them to do certain things. and like i said, when it comes to the swimming, get her into some lessons, and ask the instructor about this 'being forced into the pool' thing - then at least you have a professional's advice and statement that forcing her in is going to make things worse. at the very least, talk to a swimming instructor and get that.
good luck