I can't believe I've strayed into the sleep section: fear of what's coming I think with dc2 due in June (oh, and don't want to do my work...)
I can only sympathise and tell you what I did. When we found out we were having another I was on a mission to sort out ds's sleep. He was 2y1m and - like yours - taking at least an hour to go to sleep, with us sitting by his bed, and then was awake at least twice a night, usually 3 and often 4 times. He didn't come into our room but he did cry and shout out etc until we went in, and he needed a lot of help from us going back to sleep (ie, a long time, and all crouched over, cold, in the dark etc etc woe woe). And to top it all off he was an early waker. So we were kn'k'd. We had people on all sides talking about controlled crying etc rods for backs etc, but we just couldn't bear the screaming, and didn't want him to learn that we wouldn't be there for him. (Not trying to criticise other people here: all babies are different.) Whenever we left him to cry at all he would scream a tormented extremely upset cry, not any of those other cries we would be able to leave. It just wasn't how we wanted to do things.
So when we found out we were expecting no2 I wanted to sort things out because I was terrified about having nearly 3 years of his sleep and then straight into newborn (sorry, this sounds like exactly what you're going to have..!) His language was good enough that I could explain why I was leaving and that I'd be back. Consistency is the key (that's cognitive learning theory!), so I had rules that I absolutely kept to without having to think (very useful in the middle of the night and when v upset, stressed etc). When he woke up crying I went straight to him as usual. Gave him a cuddle and when he calmed down enough to listen I explained that we were very tired, I needed to sleep, I need to sleep in my big bed not in his, and he needs to sleep in his bed, so I'm going to my bed now. Then kissed him, said I loved him, and left the room. He would then scream out and cry and it was horrible. My rule was to go in exactly 60secs after he started crying. I used my running watch and went exactly by that, so I couldn't cave in, or stay out longer because I was cross. I even got to do my physio in the hallway while I waited (gotta grab those silver linings...) After 60secs I went in again, stroked his head, calmed him a little so he could hear me then again said I'm going to sleep in my bed, I love you, kissed him and left again. Then again pretend to go back to bed but just stand in hall, on one leg, watching the 60secs. Repeat for eternity.
First night I was up like this for 1h45m. Next night it was 45m. Then 25m. Then - annoyingly - we went away for a weekend so had to start again. But after about a week it was only 5m, and not the upset tormented screaming but more of an objection. Then he'd just need a pat and a kiss. I never believed it was possible!
Then all of a sudden he started going to sleep in the evening without us. This happened by accident: phone rang or somethign so whoever was on sitting duty wasn't there. Went back 10m later and he was asleep. So that was it from then on.
He's still an early waker, but he gets into bed happily, lies there looking at a book, singing etc and going to sleep on his own. Sometimes he's upset, and we go to him and soothe him, and then he can go to sleep himself. Sometimes he's a complete PITA and it's a battle, but, you know, he's 2... And most nights he sleeps through. When he wakes up it's usually for a reason: bad dream, fallen out of bed, needs a drink. We go in, sort the problem, and then he puts his head back down and goes to sleep.
I know I've gone on and on here, but it has been such an enormously big deal for us. I can't understate how bad his sleep was, and he's very active so the days are tiring, and day naps have always been a bit rare. And I know that I'm not describing anything particularly ground-breaking here. I guess some people would call it rapid return or controlled crying, but I've never thought there's anything controlled about it. We couldn't bear it, but it made a big difference when he was old enough to discuss things: he didn't think (I hope!) that we were just deserting him and wouldn't be there if he needed us. (Again, all parents and kids are different: not criticising anyone who did things differently.)
What you describe sounds a lot like our probs, so I hope this might give you some hope. If your dd's language is good enough to understand I'd definately recommend trying this approach NOW (ie, tonight!) and hopefully it'll be ok by the time the baby comes. Of course, everything will be mucked up then, but at least you can still say the same things: She needs to sleep in her bed, you're very tired and need sleep etc. And praise her enormously, reward relentlessly etc. (If all else fails, read her this post: it's long-winded enough, she'll prob go straight off.) Good luck, whatever you do!