i suspect that the reason she would like to retain the rights to the video is for copyright protection of her technique.
this is not a problem. just charge more than you normally would. i am sure she will understand and will pay the premium to retain control over the footage. for example: she wouldn’t want you using b-roll of a secret technique in the girl guide fundraiser video that God-knows-who will see.
this is also the secret to doing more work for her. don’t fight her on the rights issue. if you get your gander up and your back to the wall she may even pull this project from you.
just consider her to be the producer with all of the rights over the footage and yourself as a contractor to shoot, edit, and what-ever.
as i say. simply charge more than you usually would. she will pay it to keep control over her techniques.
mick