In his own transcription, MacColl (Singing Island, 1960, 32) quotes the words as 'hired your hand', not 'hired your horn'; and 'aye she grat', not 'aye she scrat'; so presumably that is what he thought he was singing. The former he apparently got from Maidment, the latter presumably from Samuel Wylie or perhaps William Miller.

That take on 'Scallater' / 'scallet her' is interesting. The word isn't one I've come across in the usual Scots dictionaries. Where do you know it from? When you say 'Lallans', do you mean the Lowland dialect or the literary construct drawn from wider sources? Although Maidment identifies no source for his text, Aberdeenshire seems likely enough; though MacColl's oral sources (and we don't know whether either or both of them had that verse) were both rather further south, in Stirlingshire. If there is a mis-hearing involved, then it was Maidment's, or his unknown source's, and dates to before Child was born.