It could be so much worse: Shadow Web by N. M. Browne. Bloomsbury, 2008.
Jess Allendon is bored with her homework so googles herself. She finds another Jessica Allendon who asks for a meet up. Not being stupid she takes her mate Jonno with her when she goes to meet the other Jessica in Waterloo Station, but when she sees a face identical to her own, shock takes over and on automatic pilot she moves forward and takes the other girl's hand.
There is an explosion and when Jess wakes up she is in a different Waterloo Station, one where the floor is made of coloured marble, and young men in purple uniforms are rushing toward her, hustling her out the door as a "Yank poppet". Jess is put in a taxi when they realise she is from a resectable household, and is driven to a grand house not far from Soho. There. she finds herself forced into the role of Jessica, sixteen year old secretary to Mrs. Landsdowne, in a house riven with politics and suspicion.
The world "Jessica" lives in is not just alien to Jess it's horrifying: women appear to have no rights, only those over thirty can vote. Jess is subject to constant sexual harrassment, and if she complains, other women assume it is her own fault. Her employers are oppressive. wages seem to be incredibly low and the workhouse awaits any servant who dares to transgress. Outside there is a low level civil war going on: in a Britain which still holds its colonies and the Black and Indian people she meet seem oddly exotic compared to those of her own world; in which the technology is still analog but an internet exists; in which the manners and mores and industrial politics seem out of the 1910s, someone is planting bombs.
Jess gets pushed from pillar to post, becomes a pawn in a game she never really understands, and falls in love with her best friend's doppleganger. Jess is only in the other world one week but it's a terrifying week in which the threats of the grey suited Security or the dapper black clothed King's Constabulary seem far less frightening than the constant sexual threat. By the time she returns home, she isn't quite the same person.
Browne hands her alternate world with a deftness of touch I've rarely seen in YA sf: she is happy to leave Jess confused and us with her. Although we learn the broad outlines of the society, we don't get to know it, and we never find out how it got that way. We know very little more about alternate London than most of us (Jess included) could describe of our own world. Browne sticks rigidly to Jess's viewpoint and as no one has time to explain the world to her, or even really a place to start explaining from (where would you begin if a stranger landed here?) this other world remains powerfully nebulous.