I disagree with what Michael wrote. I think "withered up" is quite a common expression. The "up" adds a feeling that the process is complete. For me, it's less natural to say "withered" without the "up"
Compare with "dried up". If you say "a dried up apple" it sounds like that apple has been left outside and has lost its moisture. If you say "a dried apple" It sounds as though it has been intentionally dried.
"Withered" isn't the same as "dried", but I still think adding the "up" is correct in your sentence. It shows the state she is currently in: wrinkled or smaller than in previous times. It might even be a comment on her personality rather than her physical appearance.