Unfortunate that a legal battle puts you in that position, but if this app is as important to her life as she says, she should be perfectly fine freezing that iPad where it is and not treating it like an iPad any more. It is now a dedicated appliance, not a general-purpose iPad. Buy another one for everything else.
Sucks, but, best solution given the circumstances, I think. Obviously, it'd be great if the circumstances changed.
(Edited to add backup.)