'Mountain of snow.'
No ghost (IMO) It's simply a clumsy figurative way of saying when she was alive she was more beautiful than all of the others, or perhaps more pure/virginal (but perhaps that's stretching it). These hedge poets had read classics and could imitate passingly the stuff in the pleasure gardens but some of their ideas were sometimes a bit OTT.

Unfortunately I didn't note down all of the other songs in the Robertson garland but it wasn't the same as your 1793 one as the fourth song was 'Johnny Faa, The Gypsy laddie'.

Where did you get the 1793 version reference from?

Sharp, play on words. I very much doubt it. As I said those words actually appear in the song, and it is highly unlikely Sharp was aware of the Fawn version. His own collection of broadsides mainly consists of 19thc ones, and he wasn't a burrower in the BL like Baring Gould.