Oh my, it seems like my DS has had just one sleep a day since he was born! lol. For a long time I tried to get him to have the two sleeps as he would be rubbing his eyes red raw around 4-5 pm if he had the one nap anywhere between 10 and 11 that would only last an hour to an hour and a half. A couple of times I let him fall asleep around 5 pm but then he wouldn't go to bed at a reasonable time and everyone was still awake at 9 pm
I wrote a post not too long ago asking how I could encourage DS to at least sleep longer that the hour or hour and a half he's been sleeping for what seems like eternity, and the lovely ladies said to offer him an early lunch and tire him out a bit more in the mornings. It worked the first time I've attempted it, as he slept for 2 hours. Hooray!!!! The following days he went back to 1 -1.5 hours. The other thing is that if I push him out a bit too much in the mornings, he gets overtirred and only sleeps for an hour and then it's like 12.30 pm and a whole afternoon of not sleeping!!! I am definitely not looking to him dropping his sleep altogether.
GL hun, I hope the transition is easy on your DD. It sounds like you're already making the steps in the right direction!