I recently read and liked SM Stirling's Conquistador, and I read 1632 by Eric Flint and a series of books by Charlie Stross called the Merchant Princes. All of them deal with "alternate history" or alternate timelines to familiar places and events.

I'd like to find a Young Adult book with a similar type of story. I want to pick something for my book club that gets them out of their christian fiction and cozies rut, but they don't like much "bad language" or lots of sex. (all old retired ladies)  I think Conquistador wouldn't be bad in terms of language (yes, some swearing, but not on every page or even in every chapter) but I think they will all be intimidated by the length.  My copy is about 450 pages, but it's *really* tiny type.

Any story with a woman in charge or as the hero would be an added bonus.  :-)  They aren't really crazy about supernatural/magic stuff either.  (see why I need help picking a book?!?)

There is a series of books (the Crosstime Traffic series) by Harry Turtledove that involve multiple Earths. One Earth (Prime?) has discovered a way to visit all the other Earths. Sometimes the prime Earth visitors trade for materials scarce in the first Earth, but often they try to introduce ideas in the alternate Earths that will change that society. For example, there are Earths where Communism won the Cold War, another where Germany won World War I, one where Rome still rules, etc. They fulfill your requirment of no sex, no gratitious violence, and no foul language.

All the main heroes and heroines are teens, but adults are well represented and treated fairly (not like in TV sitcoms). Check under Harry Turtledove for titles in this series. Each of  the books takes place on a different Earth, so the characters are never the same. Plus, not all the endings are perfectly resolved. Leaving lots of room for people to discuss what will happen in that alternate Earth.

For example, one of the books is The Gladiator. This story takes place in an Italy ruled by Italian Communists, but where Russian Communists really rule the world. The 'prime' Earth people have a store where visitors can play board games that teach them capitalism. One of the players is an Italian boy, whose family shares an apartment flat with another family that has a teenage girl he likes. When the store is raided by the security police, the boy, at the risk of his life, helps one of the 'prime'  Earth people left stranded in this Earth. The girl then becomes heavily involved.

I am 63, but have never grown tired of good, young adult sci-fi. I read and enjoyed most of Heinlien's early young adult sci-fi, all of which were engaging, before he started writing sci-fi with sexual themes. Try his The Door into Summer.  It is an outstanding time travel mystery, and ultimately a love story with a cat as one of the heros. 

I highly highly recommend Orson Scott Card's Pastwatch: The Redemption of Christopher Columbus.

It is an alternate history of shorter length, extremely interesting, by one of the better sci-fi author's out there, and has no objectionable material (that I recall, anyway. I can't swear that there is no swearing at all, but if there is, it was not of memorable amount or anything like that. I do not recall any sexual content, but there may have been some, if there was, it would have been hinted at more than explained.).

I really really enjoyed that one. I found it so interesting that I made my husband read it after I finished it, so that we could talk about it. I think it would be perfect for a reading group.

Plus, one of the main characters is a woman.