I take it that she burrows down for long periods of time without surfacing? If this is the case then the frog is trying to Aestivate. As long as the climate is maintained correctly the frog cannot fully Aestivate and as long as the frog does't lose weight during this mini hibernation period the frog will be fine, but I will recomend that you refrain from giving overly large meals incase she becomes impacted or the food begins to rot in the frog's stomach causing septic shock and death.
Once every three months is abnormal unless the frog is partially dormant and even then it would be once per month.