Trying to Improve my Credit any Suggestions? 😩

Hi I’m trying to improve my credit score. One of the ways I’ve tried to do this was by adding my name to my grandmothers American Express account, as one of her privileges she could give cards up to four ppl, so I became one. Using this card I’ve been able to improve my credit score through credit age and utilization at least that what it says on credit karma, I know to take that with a heavy load of salt, lol. One thing I notice though is that even though I pay the full amount I owe every month unfortunately I have 4K-5k debt balance on my report from my grandmother’s balance.

My question is what do I do?

1. 1. Is there a way to get her balance of my report?
2. 2. Do I close the account? Or 
3. 3. Is the risk worth the reward? and 
4. 4. Just pay off her debt myself? 
   5. Is there another option I haven’t considered?
5. Please any suggestions I’m grateful for your help Thx! 😁