Cassandra Wilson is described as being vulnerable and police say they are concerned for her welfare.
She was last seen at Blackburn Hospital on March 22 at 1.45pm.
She has very long ginger hair, with a slim build and was last seen wearing a purple fleece, grey jacket, jeans and trainers.
Anyone with information should contact Lancaster Police on 101 quoting log number LC-20160322-0957. Thanks