This is a good example of having to go with what the norms are for your area. If being open for 10 hours is what others are doing then you will have a harder time attracting people who don't use the 10 hours and certainly not get people who are going to pay extra for it.

A lot of the time I base things on what the hours of everyone else is in the sense of if I am open that early or that late for others then I would be much more willing to be open for this family but talk to her about ok if you want to come earlier in the morning please try to be here as soon as you can at night.

Do you have something specific in your handbook about how many hours of care the daily fee covers ie 9 hours or 10 hours. With a statement about what the fee will be fee for additional time? If you don't then I can see where the mom might have felt she was the one being taken advantage of in the sense of she felt she was paying for a full day of care - ie your open hours and should be able to change her hours as needed.