This is Irene Adler, professional name "The Woman", introduced in "A Scandal in Belgravia", the first episode of the second series of the BBCs hit series "Sherlock", which is more or less the Doyle books set in the modern day. For example Watson's stories are now a popular blog, and Holmes still scoffs at the absence of science and logic in the comments.
Like, oh, just about every version of Holmes in existence, she's portrayed as a love interest to the sexually oblivious Holmes. Holmes helps people for a living, out of the sheer intellectual joy of it. Adler's a professional dominatrix, who is decidedly not in her line of work for intellectual reasons. Holmes is basically asexual, Irene is bi, and hits on everyone, everywhere, all the time. Sherlock wears the same basic outfit at all times, Adler has an large closet. Sherlock is smart, so is she. Sherlock is Connected, so is she. Adler's sleeping with her assistant/partner, and Sherlock isn't, no matter what the fanfics say. Said assistant is, naturally, submissive, while Watson is anything but to Sherlock. Und so weiter.
Basically, she's just begging to have fanfic written about her. In fact, she's like a fanfic Mary Sue, only better written, with actual flaws and weaknesses and stuff, like her habit of objectifying people. Sherlock turns people into puzzles. She turns people into sexual objects. And then blackmails them; the letter from A Scandal in Bohemia is turned into a camera-phone, and the question becomes not merely finding it, but figuring out the password.
A brief aside: the show actually does update the themes of the Doyle canon to the modern day. Sherlock uses nicotine patches instead of opium, and the close friendship with Watson is viewed, by modern sensibilities, as very, very gay. It's a running gag in the series, despite Watson's parade of girlfriends (he was a ladykiller in the Doyle canon, and modern interpretations, led by the Ritchie films, have stived to restore him to his status as Holmes competent, ladykilling partner, rather than the popular image of a bumbling nincompoop of a sidekick). The actors admit it, the producers admit it. So we have, of course, slashfics. There's even a very, very popular kinkmeme.
Some fans don't like Irene, sez TVTropes, which confused me. Why would any significant amount of people not like h--
Oh. Hang a sec, this'll take some explanation.
"Supernatural" is a show about two denimed brothers who travel the country slaying monsters and ghoulies and long-leggedy beasties in a cool car and are more than a little codependent. One of the running gags of the show is jokes about how people think they're gay, despite their denials.
This woman is Bela, a brown-haired upper-class Englishwoman with a traumatic past who..."collects" and sells supernatural artifacts to the highest bidder. She's the amoral yin to our boys' yang. Also, she's a more realistic version of Lara Croft.
While she is attracted to Dean, the older and shorter of our two denim-clad balls of daddy issues, there is basically no chance they're ever going to be in a relationship, or even sleep together. He simply does not trust her, and for good reason. Bella is a fan-favorite character in the female-dominated, slash-heavy fanbase, for all her resemblance to, again, a better-written fanfic Mary Sue. Sex positive, competent, an occasional guest star who's a counterpart for the main characters, has her own adventures, and is almost completely ignored in fanfics in favor of slashing the two male leads.
Jo Harvelle started out the show as a wannabe monster hunter, a daughter of a hunter, with a crush on Dean. Fans didn't like her much. A few seasons later, she showed up with more maturity, but most importantly, telling Dean she wouldn't sleep with him even if it was the last night on Earth. (As it probably was.) The fanbase loved her.
You may be noticing a pattern here.
The bottom line is that whatever female-dominated slash-heavy fanbases may say, they don't want Strong Female Characters. They want Strong Female Characters who can be easily ignored for their slashfics. Though to be fair, they do this with het shipping too. Just look at the "Avatar: The Last Airbender" fandom. Or better yet, don't.