I'd have to agree with ISPYSHHHGUY about Batwoman, but my Batwoman was the Kathy Kane version from a bit earlier (1st. appearance, Detective comics 1956). Loved that costume. (Lois Lane also used the Kathy Kane costume in one of her stories.
Girls did appear in comics we consider designed for boys. One of the best examples is Katie from Billy the Cat. TNT Tom had Tina as a super powered companion. No point in mentioning the female characters in humour titles, you all know them. And as for sex appeal, look no further than Val Venture, Ace Hart's superheroine partner in Super Thriller. Have a look:-
http://www.internationalhero.co.uk/v/valvent.htm
Mind you, when Miller ran out of Cap. Marvel stories and came up with Marvelman, they got rid of Mary Marvel and shoehorned in a lad, Kid Marvelman.
Even more openly sexy were the companions of Roy Carson and Swift Morgan, whose comics were not designed for children. Silk and Silver, respectively, were drawn as very glamourous in tight dresses and costumes.
Super Detective Library ran the adventures of Lesley Shane, a glamourous detective and Buck Ryan had a sidekick/secretary, Zelda, if memory serves, who shared in his adventures. Both these were reprints of newspaper strips and I don't think they were designed for kids.
No, I don't think British comics were aimed solely at children, although it's obvious that Beano, Dandy etc. were considered as such and that's despite Clapton reading the Beano on the album cover. But comics were consumed in great numbers by young men and adults. It's just that a lot of society felt comics were beneath them. Certainly, the British comics made to look like American comics were read by more than children and pocket libraries featured ads for the armed forces, suggesting, I believe, that the military thought young adults/teenagers, to use a later terminology, were reading them.
Thanks abacus, you made me think, always a strain