If the issue is the meter reading cycle rather than there being a serious possibility of an ongoing, second leak, all she needs to do is read the meter herself every couple of days and each time, extrapolate out to one billing cycle. Then she can make a direct comparison to her old bills.
We think it may have been leaking for a lot more than a week of the previous month, based on the last time somebody would have flushed that toilet. In other words, if it was three weeks in one month and one week of this month you wouldn’t expect the same bill.
If nobody is using the toilet in the garage, shut off the main water valve to it.
Sometimes around here we are billed for water or electricity on an estimated reading - They don’t actually read the meter. If they are out either way it is usually corrected by the next bill. Do they do that round your way?