There are LOTS of religions which have dress restrictions for women - in some Assembly Of God churches the women wear no pants (only dresses), no cosmetics and they do not cut their hair and wear it "up" only after marriage. The Duggar Family (of 19 kids, Quiverfull fame) believes in modest dress for women - no pants, long skirts, little make-up etc. A LOT of fundamentalist Christian families (not LDS) embrace what they calll "modest" dress for women and there are many places online to purchase such clothing - including swimsuits. Some religions require it (both Christian and Muslim) and in other cases it is a personal belief. The LDS (and FLDS) church also requires the special underwear - in the LDS church it is only when you are married - or get "Temple Membership" that you are required to wear it - and it does restrict clothing styles - can't even wear sleeveless or tank tops or above the knee shorts while wearing it - and a traditional swimsuit is pretty much out of the question. Even religions who don't have mandated clothing requirements push "modest" attire for women - MANY Church Camps require one piece "modest" swimsuits or that the girls wear clothing OVER the swimsuit, and require shorts that fall less than 4" above the top of the knee cap and shirts be "regular" plain mens style T-shirts with sleeves 10" long or longer and high necks and sleepwear be pajamas with pants. ALL the kids cannot bring clothes or shoes with words, graphics or "offensive" logos on them.
While MOST women do not feel it is necessary to dress themselves and their their female children in clothing from 1890 and wear special religious long-underwear COVERED by leggings to be properly "faithful" it is far from rare to encounter women whose clothing choices are mandated by their faith - even in the Christian predominated good-ol USA. The Amish, Mennonite, Assembly Of God, LDS, and many independent Christian Churches ALL have clothing restrictions - some more rigid than others, but ALL focused mainly on attire and appearance for females being restricted to some degree.
I will look, I used to have some links filed of several websites selling "modest" clothing for teenagers. It can be lucrative as most of it is custom-made.
My Opinion