Flandyke Shore has been discussed here in the past, and pretty much everything said that can be without referring to the set found in tradition in Scotland (The Flanders Shore) by Andrew Crawfurd, and to the chapbook/broadside from which the song is apparently descended, The Ploughman's Love to the Farmer's Daughter. The fragment found by Sharp suggests that it's one of those stories where a cruel father locks his daughter up in order to put an end to an unsuitable relationship; disappointed suitor goes abroad; daughter dies. Need to see Emily Lyle's Andrew Crawfurd's Collection of Ballads and Songs, which has the Scottish set and the chapbook text, though.