first of all... you haven't messed her up. you had a routine that was working well... and then it started to not work so well. it just means that it's time for a change. it's hard to give up old routines (especially when they were the only ones that worked in the past!), but it sounds like she's ready to move on and so are you... so now you have to try some new stuff to see what'll work for everyone now.
i think that nursing and rocking to sleep is amazing... until it doesn't work anymore. i was nursing my boys (i have twins) to sleep pretty much exclusively until about 15mos when i weaned (night time was the last to go, so it was night weaning and full-on weaning). whereas before they'd nurse to sleep and i could transfer them to their cribs no problem, it was just getting absurd. i'd be nursing them for 8 million years, then they'd wake up in like 10 minutes, and wake a bunch through the night (one more than the other). the boob wasn't the magic bullet it once was, yet there was absolutely no other way to get them to sleep (they'd SCREAM). i think the problem was that they didn't know how to mellow out without the prop (nursing in my case, rocking in yours). soooo.... you work on removing the prop, and finding something else cozy that works.
what i did was get them good and tired during the day, then lay with them at night in a very dark room. they bopped around and played and etc... but eventually fell asleep. the first night, they continued to wake as usual (expecting to nurse back down). i did everything but. they protested for sure... so i did everything i could to get them sleepy and relaxed to the point where they could fall asleep. one of my boys was tougher to mellow out than the other... so i resorted to letting him watch a movie at 3am once or twice, in bed with me, in the dark. i know others don't agree with that, but whatever gets you through the night at that point. anyway... the first night sucked really bad. the second night sucked a little less. and by the third or fourth or something (i forget exactly) they were sleeping pretty much through the night. they definitely started both STTN very soon after, and have been ever since (they're 18mos now). now... getting them to bed was a long, drawn-out pain for a long while. the laying with them thing worked for a bit, and then started to not work anymore, so i've had to find each kid's way of mellowing out. but i've been slowly working at it and now they fall asleep fairly easily usually. i have them on mattresses on the floor in their room, which they like immensely better than the cribs. oh, and they have a bedtime routine which i think helps a lot, too (dinner, bath, read, bed).
so yeah, sorry if this was so long-winded. hope i helped. please don't resort to CIO - it's not the answer. you just need to get her off the prop, and teach her how to mellow out without it. there will surely be crying involved, but at least you'll be there with her and she won't be alone in bed in the dark, know what i mean? it's just time for a change - you've done an amazing job so far... time to adapt to the new reality! good luck!