I agree with the others that 3 times a week is just fine
Not to add another worry, but when we took Olivia to Hawaii when she was just over 2, the water wasn't our issue. Well, the waves were a little, but it was mostly the sand! She didn't like the feel and her feet being "dirty." I am not sure exactly how to do it (maybe sand from Home Depot in a foot tub?) but if she isn't used to it you might want to get her prepared for that as well. We had to carry Olivia on and off of the towels, and she would freak if she accidentally stepped down in the sand. By the end of the week she would go on it with her shoes on, but I wished she would have been more willing to walk and play in it all week long!