You can't, you have to clear it through a Restore: If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support
If you don't know her Apple ID and password and she had Find My iPad turned on you are going to run into Activation Lock. If she was a minor you will need the original receipt and a copy of the death certificate them make a Genius Bar appointment at your nearest Apple Store. If you was an adult you will need the receipt, the death certificate, a copy of the will and a letter testementary or equivalent or the executor to go with you.