Great idea to charge for the additional time and service. If anyone else who wouldn't charge for this WOULD charge for flowers or other 'add ons' it should be considered in the same light. They are asking for upgraded service. All of us say we will accommodate dietary restrictions. I doubt any of us say we'll accommodate, for free, whatever the guest wants to throw at us in the way of 'requirements'. And if we do, we all know we all complain about it.
If you reduced the rates because of an extended stay because the reduced workload was considered into that discount, then yes, charge $10/night. This has happened to friends several times...'You WILL be changing our sheets everyday, correct?' with the tone implying, 'or else'. None of my friends have ever conceded to change the sheets. You've come up with a great compromise...guest gets what they want, for whatever reason they want it, and you get compensated for it.