I'd extract the current key NOW before it's too late. I like this tool as well as Belarc Advisor.
https://www.magicaljellybean.com/keyfinder/
Next, it's no secret if you have a full retail license you can download a replacement DVD ISO. I noted that a few days ago at:
http://forums.cnet.com/7726-33042_102-5656520.html
As to the Upgrade path it sounds to me you are trying to game the system. Don't. Microsoft's activation has teeth and you may find your grandmother calling you for support.
Bob
So my grandmother has a PC on 8.1. She originally had 7 and bought a 8 pro upgrade. Then she got the free 8.1 upgrade. If she got the 8.1 upgrade would that have gave her a new product key? Like if she isn't on 8 anymore could I use it to upgrade my 7 to 8 since she is on 8.1?

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