I agree with Karen to try and move her nap up, even if it is just 15 minutes.
The earlier we put Tyler down for his nap (within reason) the longer he sleeps. For example if we put him down at noon, he will usually sleep till close to 3PM. If we put him down at 12:30PM, he will sleep till about 2:30PM. If we put him down any later than 12:30PM, like 1PM. He will be awake at 2PM.
HTH. and Good luck!