First, let me say big hugs to you--this is a tough spot but you will make it through! You are doing the right thing by seeking answers...God bless and best wishes to you in setting things back on track. :)Now, on to my thoughts...
I am as big of an advocate as you will ever meet for the Babywise program (i.e. following a routine, putting babies down awake from the very beginning so they learn to fall asleep on their own--which sometimes does involve "crying it out.")
HOWEVER...With your daughter being the age she is, even I am not sure I would advocate a straight cry-it-out approach. To me, that would be literally rocking her entire world by trying to solve the situation too quickly. It took more than a week for this problem to develop, and it's going to take more time than that to set her sleep habits on a new course. (This is just my opinion.)
I wish I had some good advice for you, but I think you need to do some research to figure out a gentler, (but still STRUCTURED) plan for where to go from here. Go to the bookstore and do some free browsing of the books others have recommended in order to find the one you want to go with...and if I were you I'd also try contacting the Babywise organization and see if they have any modified advice to fit your situation.
Whatever you do, try to put together a definite game plan for how you are going to handle the crying. If you are not consistent with what you do, nothing is going to be effective. Also, look at her nap schedule...Are there things you could change about her daytime routine that might translate into better nightime sleep?. It will probably be easier to make changes to her daytime patterns as a start. For example--when are her naptimes, and approximately how much sleep is she getting?
I have a daughter that age who does sleep through the night...She is right in between that one nap/ two nap transition. In her case, (depending on what is going on for us that day) she either takes one long nap after lunch (appr. 2 1/2 hours) OR she takes two short naps (about an hour nap around 11:00 and another hour nap around 2:00). I'm just throwing this out to give you something to compare to--not saying you should force your daughter on that exact schedule.