She came down to Earth in the guise of a grey rat, but had the ability to change into a beautiful woman or a hag with a tongue a yard long. If she visited a man at night in her beauty mode he would be sure to die. What a tease.
She also ran an oracle service for priests, offering hot tips for future success in exchange for a little sacrifice. But word got out that she spent most of her time in a tree as a grey rodent. Someone must have ratted on her.
One night, a person or persons unknown cut down the tree. She must have realized she had outstayed her welcome, as she was never seen again.