Hey A.!
I don't know if this will help, but I have a couple of suggestions. I hope it helps!!
Is she teething? My 3 year old use to cry and cry when she was teething. A lot of times once they get a couple of teeth we forget that they still have more that come in every now and then. If it is teething, I highly recommend the Baby Orajel for Nighttime. It worked wonders for my 3 year old and now for my 7 month old.
Is she a light sleeper? We have always used a fan for our girls while they sleep. For some reason it really helps them sleep longer and better. I don't know why. We just put it in the room and blow it away from them, but the noise seems to really help. You could try that.
Does she get cold easily? My 7 month old daughter use to wake up every single night at 3 in the morning. I couldn't figure out why. And then I realized she was getting cold every night and it was waking her up. So now I have to put her in a long sleeve sleeper and wrap her up in a fuzzy blanket so she doesn't get cold. I have been doing this all summer. I never thought of it before because my 3 year old is very warm natured and couldn't sleep unless she was completely uncovered and in short sleeves. Now the 7 month old sleeps at least 10 hours without waking up. But if I forget to put her in long sleeves and wrap her up, it never fails that she wakes up.
I don't know if any of that will help or not. But that is what I have experienced. Hopefully you will figure it out soon and get some sleep!!! There is nothing worse then being too tired to function!!!! Let me know what works!!!!
Good luck!! K.