Received an iPad from someone

You need to know her AppleID and password to completely erase its content. Then you can use this procedure (to have it ready for a new user):--> What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

If you don't know her credentials, only Apple can unlock that device. See how here:--> How to request access to a deceased family member's Apple accounts

Regards

Giulio

Assuming that you are able to access the iPad, this procedure should be followed to properly prepare the iPad for reuse:

What to do before you sell, give away or trade in your iPhone, iPad or iPod touch – Apple Support

You’ll need the currently associated AppleID. If unknown, as close relative of your late sister, you may have adequate knowledge be able to recover her AppleID and passcode from here:

https://iforgot.apple.com

To recover your sisters credentials, you’ll need access to one of the following:

• The primary email address mailbox that corresponds with your AppleID
• Any of the secondary/recovery email addresses that should be configured for the AppleID account
• Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with the AppleID

Unless the AppleID account has not been fully/correctly configured, or has been seriously neglected, recovery of the AppleID and password should not be difficult.

More information about recovery of an AppleID:

https://support.apple.com/en-us/HT201354

More information about recovery of an AppleID password:

https://support.apple.com/en-us/HT201487

When your recover your sister’s credentials, you would be well advised to log-in to the AppleID account from a web browser - and verify/update any email addresses and trusted telephone numbers:

https://appleid.apple.com