Welcome to the forum. You're sure it's the same RES? I really don't think the turtle hibernated for a whole year+ nonstop. During hibernation, fat stores are used up, and I really doubt a turtle has a year's worth to use (it would starve).
If you lost your turtle last April, 2006 she probably foraged through the spring, summer and early fall. When it got really hot, she probably did burrow until weather conditions became more favorable, and when it got cold enough to, did hibernate for the winter/part of the winter. She woke up in early spring/warm enough weather and has been somehow surviving until you found her.
At any rate, congratulations on the return of the prodigal turtle.

If the turtle really thin? Does she appear otherwise healthy if she is? No signs of any injury? If not, get her some proper food, and carry on. (You had her for 4 years perviously, so you must know what to do.) Just keep an eye out for any possible signs of an RI or other problems.
"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-