A two- or three-a-day nap pattern should last without much change well into the first year.
Real nap change may not occur until 14 to 18 months, when many toddlers start skipping the morning nap, or at least push it later. It makes sense; she's more active and more interested in playing than snoozing. If your baby seems ready to consolidate her sleep into one nap a day, it's better to shift it to the afternoon so there isn't so long a stretch before bedtime. Getting to that point, however, is not a one-day process. You could have several weeks of transition time. Try shifting lunch earlier for a while, and putting baby down after she eats.
Some babies spend their second year alternating between one- and two-nap days. This happens often when a toddler is in daycare part-time, where one nap a day is the norm. Yet when she's home with you, she has two. Don't worry about a shifting routine; your child's mature enough now to go with the flow.