when she signed the release and you paid her.. you own the rights to those images.
If she doesnt understand that, then she shouldnt have signed the release.
you can offer to sell her the rights of those images, but there might be a problem with the sets you already sold, since she now owns the rights to those set of images.. In other words she now owns the rights to those images and she might be able to sue the webmasters who bought them. There maybe some kind of loophole there.
Really consult a lawyer before any decision is made, and make sure all ramifications of selling those rights back to her are defined.
Also these are costs that you will have to get reimbursed on. So she will end up paying dearly for changing her mind
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