That is about the age where she needs to find her transitional stage. Going from two naps to one is not easy for a little one, and it's going to take some trial and error. I found with my son (who was 15 months old at the time, after about two months of wanting to just throw myself off a cliff) that I had to "shut down for a few days". If it's possible, I suggest it to you:
~ Take about three days, and just play at home. If you get in the car, or force her to nap at a given time because you have to be at a certain place at a certain time, then you are never going to see what her natural clock says.
~ Play, play play. Normal play, nothing out of the normal. Do as if you would if you were just snowed in. Take note when she starts to get tired. For my son who regularly slept from 11AM to 12PM and then again from 3PM to 5PM, this was 1PM. We went into his room together, and laid down to "rest". Within 10 minutes he was asleep. He would sleep anywhere from 1 hour, to 4 hours depending how busy our morning was. He did this all three days, so I knew that 1PM was his time.
~ Try to plan your days around this one nap. I did not get in the car until 1PM because I knew if I got in after 11AM, he would fall asleep for 10 minutes and that would be it for the whole day and I have a monster on my hands. There were many times I got in the car at 1:00 and quitely transfered him to his bed. He usually woke up, but if I laid with him, he would go back to sleep.
~ There were many times where he would sleep longer than 4pm, which would make him want to go to bed later. I woke him up at 4.
~ If she just won't sleep (some kids don't), but gets cranky, then make a special quite time. When my son turned three, he started preschool, and had to give up naps. He still needed them, so we moved up bedtime an hour (which helped A LOT) and we had "special tv time", where he was allowed to lay on the couch with his favorite blanket and pillow and watch one hour of whatever he wanted (usually Sesame Street). He was not allowed to get up, talk, or play. Just "rest" time. If there were other kids, they rested to, the whole house rested. Usually it gave me the break I needed, and his little body enough rest so that he got through the day without being mr. crabby pants.
I dont know if i agree with rock because my daughter is 14 mos and use to take 2 naps a day also. She takes one around 11-12 am and is up within 2-3 hrs, best part of my day :) and she USE to take an evening nap. Not anymore, so we put her to bed between 730-830 and shes still up at 7 am. Even when were out and shes up until 10 or so she still gets up at 7 something. I hate it!
I think she's sleeping about the average amount of time - 12 hours for a child 1 - 2 years old.
7 at night seems quite early to be putting her down - maybe if she went to bed at 8:30 or so, she might sleep a little longer in the morning and take a little longer nap?