Depends on a lot of things I think! You do have to take into consideration her personality and needs. I mean, if she's not ready, then she's not ready!
That said, we made the jump to 1 nap at 11mos with no problems and minimal OT. But I just knew DS2 could do it, he was already doing a short am/long pm for months and handled a really long am A time no problem. So I knew. I wouldn't have pushed him if I didn't think he could.