Hi Amy
Yes as KDee says I did do this recently, basically I just pushed the nap later by 15mins every week, & kept him up til nap time regardless of when he woke. So to start with we were doing 11-1 with a 6pm BT. Then it was 11.15-1.15 & 6.15pm BT & so on, until we got to a 12.30-2.30 nap and a 7.30pm BT. It took a long time & he got very overtired in the process, but it most definitely helped with the early starts. You could do it more quickly i.e. every few days if you feel she will cope with it ok - we started off like this but Oliver got very overtired so I slowed it down & pushed 15mins later per week.
WRT when you should start capping the nap, I would say if you can get the nap to start consistently at midday at the absolute earliest, then if you are still getting EW or long NW, then you could perhaps look at starting to trim it down as you push it out towards 12.30, so you do nap from 12.15 - 2pm, BT at 7pm and then nap 12.30-2pm, BT at 7pm. Something like that.
What do you think?