I have read that for some kids it can take awhile. So one day may be 1 nap, then the next 2 naps, etc. For me, we went to 1 nap at 13 months because we were having to work too hard for the 2nd nap. So it wasn't even worth trying for a second. However, some babies really need the 2 naps til closer to 18 months.
If you want to just go to 1 nap consistently now, I would try to keep your lo up til at least 10:30 or 11, by slowly (15 minute increments) moving her nap time back. So if she can go til 10 tomorrow, then 10:15 the next day, etc. Also, the duration should slowly lengthen as well. My dd only napped 1 or 1 1/2 hours for the first few weeks of the 1 nap transition, but then she consistently went to 2+ hours.