{{{{{{hugs}}}}} as it sounds like you're really in a bind! It really does sound like a prop issue to me - especially since you've "always" had to sleep with her if/when she wakes. It sounds like she's never learned how to go back to sleep on her own, and as she's gotten older, it's only gotten worse.
I know you said that pd, wi/wo and gw don't work, but honestly, those are the only things I know to try. I would say if she gets so upset to the point of vomitting with wi/wo, don't do that. But do try gradual withdrawal - it may just have to be super, super gradual. I'd start with moving a mattress into the room (or do you already have a bed that both of you can sleep on there?). And start with sleeping with her.
Does she have a lovie? This is a good time to introduce one if she doesn't. So you, lovie and dd all lie down together and go to sleep. And, because I would say she's never really been an independent sleeper, you may want to stay with her all night long - so you're right there for any NWs. When she wakes, have a key phrase that you say (something simple 'it's time for night night...here's your teddy/blanket/etc.) and don't waiver from that. Then after 3-5 days (or a week maybe), prepare her that you will still sleep in her room, but you'll be right next to the bed, and she'll be in the bed with blanket/teddy/lovie. Then move a mattress in there so you can sleep on the floor next to her bed. And repeat the same process you did while you were in the bed with her. Then every 3-5 days (or a week), move the mattress closer to the door.
Each time, use the same phrase to comfort her. At this age, consistency is crucial. Each time you vary the routine or go back in to bed with her or take her in your bed, reinforces the waking habit - she will then think the next night "maybe if I cry and scream enough, mommy will come back into bed". Tracy recommends that parents alternate shifts, each parent taking 2 nights on and 2 nights off. I would be prepared to get little to no sleep each time you withdraw further. If you can stick to a well thought through plan, I really do think it will work. There will be lots of crying, and you may have nights where nobody gets any sleep. But the more consistent you are, the better it will be in the long run.
The other option is to keep doing what you're doing, but then you'll need to be there for every NW and sleep with her.
hth
michelle