Yeah it charges when it's connected, and iTunes opens with a message that says "iTunes could not connect to the iPhone “iPhone” because it is locked with a passcode. You must enter your passcode on the iPhone before it can be used with iTunes." with the option to select Try Again, Cancel, or More Information, which links to this article.
I have a Mac but I plugged it into a PC and it shows the phone, but nothing is there when I try to open it. Yeah I think she either set up a passcode without knowing it, or one of my cousins messed with her phone and did it. She wouldn't know how to setup iCloud, so unless someone else turned it on then probably not. I asked for her email and password, so once I get that I'll check if she did.
Yeah the iPhone showed up, but when I opened it the folder was empty. I don't know if there's a different way to get into the phone, since I normally use a Mac.
Yeah I know, I asked everyone who's used her phone if they setup a passcode, but they all denied it, so someone set it up and either didn't want to tell me or forgot. Or my grandma set it up and didn't even know what she was doing, which is highly likely haha. I'll have to double check if the phone is still under warranty or not, hopefully Apple can help!