Hi
have you got the room totally blacked out? I found mine would start waking early if there was even a chink of light getting in, and even when I felt like it was still night time.
Is she waking early because she's hungry? You say if she feeds at 3am she sleeps later, have you tried a cluster feed before BT? Or a DF?
It could also be that when her naps were not so good she was able to sleep a longer night...but now that naps are longer she is unable to sleep a longer night. Some LOs do have quite short nights. Mine wouldn't sleep more than 10.5 - 11hrs overnight no matter what (and it was 11 if I was lucky). If this is the case you may need to alter the routine for a later BT and later WU. Or if you feel that her mood was okay on shorter naps then you could reduce the length of one nap to see if nights lengthen - this is not always possible as LOs need day time sleep and reducing naps can obviously result in OT too.
A few ideas there - see what you think