According to the description of the official music video for the song "Fight Like a Girl", Emilie Autumn was admitted to a "Los Angeles high security psych ward" in 2007. I presume that she remained there for a few months for three reasons:

1. In the book, there's a paper which states that the patient will stay for at least 72 hours.
2. Based on how deteriorated her mind has become by the end of the book, Emilie Autumn's stay lasted for quite a while longer than 72 hours.
3. Based on her frequent output of albums, as seen in her discography, and assuming that she had to be out of the psychiatric hospital for their releases, this happened in the time span of less than a year.

According to Wikipedia, as well as myself, Emily-with-a-y lived and was committed to the Asylum sometime during the Victorian Era, i.e. the 19th century. This has also been confirmed by Emilie Autumn herself in an interview with L.A. Weekly. While I'm not 100% certain of the year that this character was committed, on one of the sliders on the main page of the Asylum Emporium, "By lunatics for lunatics since 1845" is written. This could either hint at the year when she was committed or the year when she and the other inmates usurped the Asylum.

As for the ending, from what I'm able to recall, Emily-with-a-y and the other inmates jump off of the burning Asylum while singing "Goodnight, Sweet Ladies" and die. After that, we cut to Emilie Autumn in a modern day psychiatric hospital where she finds that the letters she has been reading have been replaced by napkins, pieces of toiletpaper and the like. Her imagining the letters seems more probable than someone actually going through the trouble of replacing them all for no apparent reason. She panicks, causes a disturbance, is forcefully drugged and faints. Then, during the last chapter, she wakes up in a strange room which doesn't suit the description of any previous one. This chapter is most likely a hallucination altogether. We end on the sentence "I AM THE ASYLUM" written in mirror writing. These words imply and confirm, in my opinion, that Emily-with-a-y was merely imagined by Emilie Autumn. She used Emily-with-a-y's story and the letters as a coping mechanism and as inspiration to remain strong in spite of the terrible circumstances; hence why she panicked when they no longer existed.

To some, this sentence may seem eerie, but since books usually end on that sort of note just to sequal-bait, which I don't see Emilie Autumn doing, I would like to think of it as a bittersweet ending. Perhaps this is when she realises what's real and what's not. Perhaps this is when she hits rock-bottom and begins the climb towards a healthier way of thinking and living. I also suppose that, since the mirror writing almost looks as if were written from the outside of the room and she's in a world of semi-fiction and semi-reality, the last sentence could be telling her that it's her time to help others in need by performing and telling her story. Ultimately though, I think the last sentence was left somewhat vague intentionally so that the readers may interpret it however they wish. So that you may be inspired by her story to keep fighting your fight, whatever it might be. I hope this has been helpful to you.

As I understand it she was in a psychiatric hospital several times, and at some point was on suicide watch. Since there's a huge amount of variability between these nobody is exactly sure where she was or how true her story is.