How do you think the mother-in-law has fixed the swimwear?

Well, I know you might think you have a "real Problem" on your hands, but I find it quite laughable. She's your wife, if you want her to wear those, then it should be fine with your mother-in-law. If not, tell her you didn't ask for her opinion and you would like the bathing suits back. (of course in a respectful manner)