There’s def. a difference between OWNING footage and having RIGHTS to it. It sounds to me that you OWN it, and she HAS RIGHTS to it…Therefore it is yours to sell AFAIK. Assuming you’ve already turned the footage/edit to your client, they should be ale to give it over to the third party.
Frankly though, you need to ask yourself how bad you need the $100 compared to the time and headache of dealing with this after the fact. If you’re going to shoot for charity, donate the footage and BE DONE WITH IT. Let them do what they want with it for their purposes. If they sell it for a Kraft mac n’ Cheese commercial, you have a problem.
hope this helps, good luck.
https://www.triaxproductions.com