According to her bio at Sharing a Universe, from which she is on loan:

Princess Lynette was always the rebelious daughter in the Sheridan family, having far more interest in learning fencing and magic than in finding a respectable royal husband. This eventually lead to her father arranging for her to marry a prince from a neighboring (and rather damp) country. Upon learning of this Lynette escaped the castle and, with the help of a magically powerful group known as the Chor, fled to the one place she thought her father could never find her: Earth.

It is unlikely that the Earth on which Lynette has sought shelter is the one on which the other characters live. She was teleported into the 11th-Century Wodeskog by the hamster Skipper, who gained this ability as a result of an incident involving pink fog. Because she has been pursued by a group of park squirrels in open revolt against humanity, she agrees to help Menjou to defeat them.