Don't worry (easier said than done, I know). Babies eat when they are hungry. Some babies/children have patterns to their eating. Others seem to be random.
For instance, my son was breast fed every 2 hours and had to nurse for 45 minutes. My daughter was totally different. She was a quick nurser and ate whenever she saw fit. There was no 'schedule' and no set amount of time in between.
The only cause for alarm would be if your daughter lost weight - which doesn't seem to be the case.
Relax. You are doing fine