I was wondering the same thing. We had 4 leased cars in the family for many years. I never heard about a lease option where they checked the mileage monthly.
It is true that they give you a yearly limit, in which you can pay penalties if you go too many miles.
But that's not what she said. She specifically said monthly mileage limitations.
BBM
But she seems to be a bit of a "concrete" thinker. If she had decided to look at the yearly (or total lease length) allowed mileage on a monthly basis to avoid going over (as others have said they sometimes do) I doubt she'd deviate from that way of thinking. So to her, if it's 1 day before the end of the month and she's used up her "monthly allowance" of miles, she can't drive the car. Of course, most who think in terms of monthly miles on a rental know it's easy to cut back in some other month and it will average out. But I don't think she thinks that way. To her there IS a monthly limit.
JMO