I think it's pretty normal, we had hugely disrupted sleep around 15 months. I think they're starting to learn about intentions, and that what you want (to leave the room) is different to what she wants (for you to stay in there forever).
Re the 2-1 transition, it will be bumpy but she will get there. Is there any kind of AP that works for her? Will she ever nod off on a car drive? I'm wondering if she could sneak a 5-10 mins catnap mid morning, and then do a big nap after lunch. The good thing about going to 1 nap is that you won't have to have that battle twice a day!
Can you do a kind of gradual withdrawal with her? Once she is calm take your hand off her bum? Then take a step away from the cot... then in another minute, take another step, etc? The other thing I do with Stan is get him totally calm, then say 'Mummy has to do a wee, I'll come straight back.' Then go out the room, then go straight back in and calm him down. I would keep doing that until he was staying calm. The aim was for me to have him be calm and me go back in to him. I still do this - even when he goes down totally calm, I leave the room, tidy up for a couple of mins then go back in for 'one last kiss': I want him to feel like he doesn't have to cry to get my attention. It seems to be working (at last) too: now when he needs me he just calls 'Mummy?' unless he's had a nightmare or something of course.
Anyway, sorry for the ramble. Had a glass of wine this evening (see my other post), and feeling a bit wobbly. Hope this helps a bit.