This is so frustrating. It's much easier to prove that something exists than that it doesn't. I'm going to put in the whole 'verse' - maybe she modified it from something else. Of course, the whole thing is completely irrelevant, but I do hate not knowing.

Sheila, dark Sheila, what is it that you're seeing?
What is it that you're seeing, that you're seeing in the fire?
I see a lad that loves me - and I see a lad that leaves me,
And a third lad, a shadow lad - and he's the lad that grieves me.

It has been suggested that, if not traditional, it may be from vaudeville... Please keep thinking for me.