Avery Edison overstayed her Visa the last time she was visiting her girlfriend in Ontario from the UK. When she tried to get into the country through Toronto's Pearson Airport, the authorities flagged her and are now holding her alone in a male-only jail cell.
Edison and her girlfriend have been livetweeting this whole insane ordeal. While Edison certainly understands why Canada is wary of her entering, she brought her UK lease and purchased a non-refundable return ticket as proof of good faith and intention to go back to the UK on time.
You can check out the whole Storify'd version here.
Her girlfriend has been able to see her during visiting hours, but no word yet on whether they've been able to get much help. According to the sources I can find, how correctional services handle post-op trans* people is case by case, though there is precedent to allow a MTF trans woman to stay in female prisons. Various sources from Google say pre-op trans* people will likely stay in solitary or will be placed in the facility that matches their genitals.
I'll do my best to update this as we get more information.