"Are there any more modest places to buy bathing suits?"
I got a fabulous suit at Macy's. Very expensive, like $90.00, but part of the money goes to breast cancer research (I can't explain this, but that's what the tag said.) I bought if for vacation and didn't use it, hubby said I could bring it back,but I said, it's the most comfortable bathing suit I ever put on, I'm keeping it.
Macy's always ruled for suits, and I see Gottex an Israeli maker is still making them. I had an excellent suit they made years ago. As I said I really am a prude, so all these suits are very modest. The new one is not Gottex, but I'd always recommend them, the last one I had I got years of use out of, and I did alot more "bathing" in those days.
As for little girls, I don't know. My daughter's aunt always used to get her a superclearance suit for her January birthday, and they were always fine.
You might do OK at old Navy, although I wasn't thrilled with their selection recently. I did veto many suits for my girl during those 'tween years. Clothes shopping was always brutal during that time. We often nearly came to blows in the dressing room!
Also you might try a Models or some other sports place. When my daughter was (very briefly) on a swim team I had to buy her a couple of pretty pricey suits. But they were cool looking and one piece.