Hi there. The problem is that your DD is sleeping so well at night and in the early morning that she's packing in so much sleep there and fighting sleep in the afternoon.
Instead of putting her right back to sleep after that 7am feed, I'd suggest keeping her up for 45 minutes and seeing if she will then nap from 7:45/8 until 10 (next feed). Basically, at her age, you do want her on a 3 hour EASY - eating approx every three hours and probably have about 45 minutes A time, at most an hour, at her age.