According to George Ellis's <<http://books.google.de/books?id=IdATAAAAQAAJ&lpg=PA403&ots=CTMWEtUjX8&dq=lassokie&hl=de&pg=PA403#v=onepage&q=lassokie&f=false|book>>, *Specimens of early English metrical romances*, »Lassokie« is a Western Scottish diminutive of »lass«, i.e., girl.