I do assume that SE Inc. respectively the OP is telling us the truth, and that there is some sort of agreement between the two parties. 

But let me say this: you start with...

> We sincerely hope she remains an active member of our community. 

To then go:

> In recognition of the mistakes that led us here, we invited Ms. Cellio to apply for possible reinstatement on all six sites following our new reinstatement process. 

Honestly, together that reads naive at best. But it rather feels like a bully who challenged the wrong person and who still tries to put up their own rules, to then blame the other party who refuses to follow said rules.

If you really want her to stay because of her great contributions, then ask yourself  why you start with ignoring her objections about the process you want her to go through. To give her back something she earned from community members electing her. And which you took from her in the most dubious way possible.