Sorry to hear about your Mother.
You are better off just restoring it. Anything purchased under her Apple ID (doesn't sound like it would be much) will need updating eventually anyway, and you can't do that without the ID.
If it is version iOS 5 or newer you can do it under Settings > General > Reset > Erase all Content and Settings. It will go through a setup where you can enter your Apple ID and other pertinent information. You need to have a wi-fi network available.
If it's iOS 4 or older you'll need to connect it to a computer running the latest version of iTunes. It will want to update to the newest iOS, and unless you have a good reason not to (like you really want to
jailbreak) you might as well let it. Be prepared for it to take a while. You can do it this way with the newer iOS version as well.
To tell what iOS version you are running check under Settings > General > About > Version.
Good luck.