It usually is- but as they get older things can muck you around! For example apparently when you are on one nap anything under 2 hours is OT! Weird! I would be guided more by how she is after the nap- crying really upset, or happy to be awake. Have you tried resettling if she wakes up crying? I sometimes will APOP (accidental parenting on purpose) some more nap if my gy wakes up crying- it often works.
Not teeth or other discomfort? This can cause night wakings and nap busting?