Same here. I've been using that "feature" to check how long the maid stays when she comes by to do weekly housekeeping.
Now I know how she can afford an iPhone, she charges for 3h but stays 2h!
Untill you knew how long it took her, were you happy with the quality of the cleaning and the price you were paying? If so, try not be be bothered by her "profit margin". If not, renegotiate the fee, or find someone else to do the job.
With all that said, are you paying her a "living wage"? For Alameda County, California that comes out to something like $24/hour for a single adult supporting one child or at least $11.50/hour to support just the working adult.
Of course people working jobs like house cleaning or computer consulting cannot typically get billable hours for 40 hours per week due to scheduling difficulties and travel time, so the hourly rate needs to be higher to account for that, or as your cleaner may attest, the "billing time" might be longer than the "working time". Other ways of offsetting this it to impose time minimums (at least two hours per job) or charge for travel time or distance. Considering that the IRS has a standard car expense of $0.56/mile, if someone is driving 60 mph they are generating an expense of $33.60/hour. Granted, the IRS is very generous on this expense calculation, but the actual expense for most people is probably close to at least half of that.
There are very few people getting rich cleaning houses.