I would let her sleep as long as she wants Nae.
Perhaps you could try something like this
Breakfast and BF when waking
Snack at around 9-10
Lunch at 11am then BF to sleep or if still awake put her down and see what she does.
Afternoon snack around 3pm
Dinner 5pm-6pm then bath feed and bed when she is ready.

You probably have an extra BF or two in there.

It's a tough transition from 2 sleeps to 1 sleep. I have followed Tess' lead. It helps that she has the distraction of her brother to keep her amused.
Another thing to try is perhaps put a morning walk in around sleep time and see if she sleeps in the pram? You could either try and transfer her from the pram or let her sleep in the pram?

It will get better Nae