Hi there, we have just gone through similar with my DS who is the same age and also a bigger baby (12lb 5) He was only taking 3 oz every 3 hrs but he was fussing after these 3oz and wriggling, shaking his head from side to side and kind of grunting. He then wouldn't take anymore milk after that and was hungry earlier.
So we changed to no 2 teats and it has worked a treat. He now always takes at least 4oz and often 5oz and he never fusses or squirms taking his bottles now. So maybe you could give the faster teat a try and see if DD will take more milk then. If not it could be a growth spurt so she is wanting to feed earlier.