The Parallax effect

Jessica Cruz has suffered from crippling anxiety for years, to the point where she was unable to leave her own home. It was until she became Power Ring's ring bearer that she was forced out of her enclosure. In time she was given a Green Lantern ring. But her inner demons were still there and she unknowingly was tainted by the Power Ring from Earth 2. This was all Sinestro needed to expose her to the Parallax entity, turning her into her new host as Hal Jordan and Kyle Rayner were in the past.