Bypassing dead relatives Apple ID?
It is likely that you will need to prove to Apple what has happened. EG you are now the legal owner of the iPad and have legal access to her account. 

Call Applecare and ask them what the procedure is for these circumstances. I suspect (if they can help) it may involve a death certificate, a copy of the will and a notarized letter from the executor of the estate giving you access.

But then I am guessing...