This discussion may contain spoilers!
We know Lily didn't die in the dress that was left torn in the closet, and seen in the picture of her in the bed with Crane.
At first I wasn't sure about how "deep" (forgive the irony) Crane did dive into the fantasy (I thought maybe he just wanted to recreate the fantasy for the pictures, which would be a twist to make him look less sick and everyone would feel a little sorry/pity for him), but after replaying Lily's body investigation scene, upon mentioning to Crane she had track mark of mundy drugs usage, he got really worried about diseases, implying he in fact had sex with her and was actually worried about the possibility of having been contaminated with some DST. (Which now I think would be just effing deserving).
Anyway, we know that Crane had sex with her in the bed, wearing the... lets call it, "fantasy dress"... and, due all the blood, that Lily literally lost her head (being cut or falling off, if you believe the ribbon theory) in that very bed. But, as Bigby points out, the fantasy dress has no blood in it, so she must have died in the clothes we found she using when they dumped her body on the river.
Note that the dress is not perfect because it's not part of the glamour. It seems that it worked just for her flesh and bone. That would explain why when she turns back into her true troll form she's still dressed as Snow.
Now lets try to make sense of this... Crane striped Lily naked before/during the sex (in the pic, we see his hand up her skirt, as she's laying down in the bed, surrounded with flowers, etc), tearing up her dress during the act, then him or most likely her leaving it in the closet. And, finally, as she was dressed like regular Snow when she died/was killed, she must have dressed up before going back to bed... after Crane just had his way with her?...
So, can anyone come up with a theory on why, after having had sex with Crane, Lily while still glamoured would dress up as regular Snow and go back to bed? That's how far I could get with the facts. I'll comment how much further I stretched my conclusions into seemly crazy theories...
Everybody, please feel free to let me know what you think about my little investigation, the theory I'm about to post, and if you have your own share it with us. :-)