Mine both dropped the second nap around that time and kept their morning one. It gradually got a bit later - around 11 until around 3 mths ago and now they both go at about 12 adn they are 23 mths and nearly 3 1/2!! J still sleeps for around 3 hours and once we cut out his afvo nap he was one that started sleeping alot longer!
Good luck - just go with her cues - when I dropped his day sleep it was still gradual because some days he still clearly needed it.