I see that there isn't much activity over on the Parkinson's Forum. I did some research to try to answer your question as I can see you are terrified by the prospect.
Your risk for early onset PD (under the age of 60) is very, very small small. There is a slight increase in risk if you have a sibling or a parent who had "early onset" PD. Instead of 1-2% risk for the general population, your risk would be 3 or 4%.
This is only if your sib or parent has "Early Onset." AND there is essentially NO increased risk for a relative more than 1 degree away. Your great aunt is 3 degrees away (also known as a third degree relative).
So, Shelly, I can't see that you have any appreciably increased risk for developing Parkinson's disease, than any other person in the general population. You're in the clear. I hope that reassures you.
Sorry, about not doing the research earlier, but I thought you would find a quick answer on the other forum.
Quix
Sorry, I would have to do some reading. Why don't you go onto a PD site and look at the family risks of it. A great aunt is not a very close relationship.
There is also a Parkinson's Disease forum here. I'm sure they could tell you.
((HUGS)) Quix