We had trouble with Jonathan sleeping at night. I always checked the following things when we had trouble: reflux medication dose (if it got too low, he would have trouble sleeping at night (but was OK for naps), hunger (I would give him cereal shortly before bed and it helped the reflux and the hunger), pacifier (we had to keep 2 in his room because if he lost it and woke up, we couldn't get him back to sleep easily). We never did co-sleeping because I never could sleep with a baby in the same room as me. I also followed the "Healthy Sleep Habit, Happy Child" book by Dr. Weissbluth. It hasn't steered me wrong yet...even with Alexander at nearly 3 years old it gives me lots of great tips.
If you can't tolerate any version of cry it out, waiting any period of time knowing you're going to go in is probably just teaching her to cry until you come back. I think for cry it out to really work, you have to be pretty committed. My kids both have pretty distinct cries when something is wrong of if they're just complaining. And, when we decided to let them cry (provided the other issues were already addressed), we only went in if it was a cry for something wrong and ignored the "protest cries". Jonathan cried one night for a few minutes and then gave up and slept all night. Sometimes he still will give some complaint cries when he goes to bed, but they rarely last more than a minute (literally like 30 seconds after we shut the door).
Good luck! Not getting sleep is hard. And, sometimes, you just have to do whatever you need to to get some sleep in the short term and try again a few weeks or months later. Highly recommend the book though - it's supportive of all methods (crying or no, co-sleeping or no).