We were on one nap from about 11/12 months and reasonably settled on it by 13 months. I think it's important to remember that every LO is different and whilst some will keep two naps until 18 months, others are perfectly happy to change to one nap at 12 months. It's a transition period anyway, it doesn't have to be all or nothing. You could have one or two one-nap days a week and do two naps the rest until she can manage with one nap every day?