C.K.
it sounds to me like its possible she is just waking up in the night and unable to get back to sleep.
think about it...you wak up slightly at night, roll over, get comfy again and you are asleep in a second. you may not even be aware that you have woken, you just move, and thats it.
if she has never had to get herself back to sleep...because you have always been there to comfort her, or she has your breast as a comfort, then its going to scare her and make her scream.
she needs to learn to soothe herself back to sleep....CIO is the fastest way to accomplish that...but if you don't like that option, talk to her dr and see what he reccomends.
also...if you don't think she is tired at 7:30..push bedtime back by a half hour. if you put her to bed when she is not tired...its possible that she is just taking herself a little nap, and waking up later because she really isn't ready for bed yet.