A.H.
It sounds like she's really trying hard to learn how to fall asleep on her own and she hasn't mastered it yet. Its a really tough skill! I know my husband still has a hard time with it! ;) I was VERY opposed to letting my son cry at all. But he had a really hard time (much harder than what you describe) and I was in a different situation- he wasn't getting enough sleep, and we felt it was cruel not to help teach him how to sooth himself to sleep. We reached a point where nothing we did could help him either- and so that was how I became open to laying down some boundaries for what happens when it's time for sleeping. I agree with you: consistantcy is the key.
I think as long as you have a very regular bedtime and regular naptimes, it's fair to teach your daughter that bedtime is bedtime, and she can now learn the skills to transition herself to sleep.
If you are open to it, the method we used with our son was to go through his entire routine very very consistently, and then finish by telling him "now it's time to sleep".
If he fussed, we timed him for 5 minutes. If we ever hear him, it's usually a few peeps and then he settles. If it goes on for 5 minutes, we go back in the room, say "mommy's here. It's time to sleep." and usually he's standing so I gently help him down to a lying down position. We let another 5 minutes go by. This way we are never leaving him to feel abandoned- if he's having a hard time, we are a consistent presence. The length of time never gets longer so he's not left wondering what's happening, but we are giving him a solid 5 minutes to work out how to calm down. The whole process is usually less than 10 minutes but he goes down fine about 95% of the time. Some days are just different! he might be a little overtired or learning something new or teething, so he needs to blow a little steam to wind down. There's a site called askmoxie which talks about how some babies increase stress by crying and some lessen stress by crying. Every baby is different. My son definitely winds down- he never really full on cries but rather fusses in little bursts.
I hope this helps you!