If demand feed, does she take more at some feeds then others? I found that my kids followed the same patterns as BF children even though they were FF. The might have 1 or 2 big feeds through the day and a few little ones, and often cluster fed through the afternoon, then a bigger feed at night before bed, and 2 or 3 feeds overnight..

Maybe the timed feeds, she just isn't ready for it.. Maybe another 1/2 hr when she is ready, she will take it on board.

You will both settle into a pattern soon..