I think its worth a try if you are getting the long NW's Amy. I think if you cut the nap down a bit you might need to be careful that her A time to BT isn't too long though, as you don't want OT to come & bite you in the bum!
I know when we work on capping O's nap (which is likely to be fairly soon I think) then my plan is to gradually push out his nap from its current 12.30-2.30 so it starts at 1pm & ends at 2.30pm with a 7.30pm BT. So he'll be doing 6hrs A / 1.5hr nap / 5hrs A to BT. You might find that 5.5hrs either side works ok too.
I think if you do cap though, I would try & stick to it consistently for a good week or so & keep the same A times too & then you'll get a feel for whether its working or not.
HTH.x