Thanks for that. Somehow I overlooked the fact that Mrs Russell's text was printed in The Journal of the Folk-Song Society, vol VIII (issue 34) 1930, 201-2. It goes as follows:

Hark, says the fair maid, the nightingales are singing,
The larks they are taking their flight up in the air,
The small birds and turtle doves on every bough are building,
The sun is just a-glimmering, Arise my dear.

Arise, my fair one, and pick your love a posy
One of the finest flowers that in the garden grows.
Tis I will pick you posies, both lily-white pinks and roses,
There's none so sweet a flower as the lad I love.

Oh why should my true love be banished from me,
Or if he should die and I shall never see him more.
It is my cruel parents that look so slight-a-ly on me
Because of the colour clothes that my love wears.

Mrs Russell would be Julie Murphy's source, then (the last couple of lines would clinch it, I think) but via the Journal, presumably, rather than The Foggy Dew; and with the first verse introduced from elsewhere and some minor alterations made, perhaps inadvertently.

Miss Gilchrist's comments on the tune (Journal, V (19) 1915, 176-7) don't actually identify any of the "(Irish) folk tunes" to which Lover's song (which I haven't heard) bore, in her view, a resemblance, so I don't know how far we can extrapolate from that to include Lemady.

It's perfectly possible, of course, though it's all a bit vague at the moment. As to Frank Purslow's suggestion that the song might be "a translation from ... Gaelic", we'd need more than just one person's hunch by way of evidence. Still, you never know.