I would definitely rule out any health issues/reflux/whatever, and if you can solve that or there's nothing to cure, let her cry for the minute (or 5) and then fall asleep. I was determined not to let DS CIO and was horrified whenever he started crying. It was exhausting. Finally, when he was around 1, two things happened: One was that he dropped one of his two naps, and actually started sleeping 3 or 4 hours every afternoon. If your DD is only sleeping 15 minutes at a time, maybe the nap won't be so long, but I'd expect a half hour, at least. The second was that he started crying at night after I got him down. He was never too easy to get to sleep, but something in our routine had to change. Once I started doing things a bit differently, it worked fine. One of the things I did was start feeding him right before bed to make sure he was as full as possible. (He wasn't eating solids yet. If your DD is, give her something filling. IDK if BM is more filling than, say, an avocado or something like that, but it can't hurt to try.)
Something else that jumped out at me... Lots of moms have come on here for advice on how to deal with the older kid when a new baby comes along. Across the board, the advice was to tend to the older kids first, then the baby, even if the baby is crying. That surprised me, as most here are anti-CIO, but it made sense. They said that the older kids know consciously they're having to wait til the baby is settled, and they start to feel resentful and more needy of attention. If they know they, too, are a priority and can see that they come first sometimes, they don't feel as insecure and the baby isn't any wiser to know that the big kids are getting their needs met first.
You've gotten some good advice here. I hope you'll find it in yourself to give different things a try (and give them a chance to work too -- it won't happen overnight) and that you can find a good routine that works for all of you. And once you do, know that something else will change and you'll have to do it all over! ;-)
ETA: I got distracted by DS and lost my point in there. I don't think what you did was CIO, and at around the same age, I *had* to let DS cry a little at night b/c that was the only way he would actually get to sleep. I didn't like it, but it didn't last long once I stuck to my guns and stopped going in. Going in just upset him more and got him distracted, where I think with leaving him alone, he would cry a bit to get out the last bit of energy from the day, and then was able to unwind. Having us around (even now) is too stimulating for him to relax sometimes. He is now 3, and gave up his nap, but apparently still needs it sometimes. We do quiet time, but if he moves around too much, he has to go in his room by himself instead of staying with me. The days he goes into his room, he naps for a couple of hours at least 90% of the time. The days he stays with me, he doesn't sleep 100% of the time.
Edited by swd12422 - 5/24/11 at 7:18am