While to this day no grass will grow Where she lies low: I planted daisies there a year ago That never blow. (158-161)
Lizzie is describing how grass won't grow on Jeanie's grave. Even the daisies Lizzie planted there won't "blow," or bloom. Why is this? Was Jeanie's body so corrupted by her contact with the goblin fruit that the soil on top of her grave won't support plants?
But who for joys brides hope to have Fell sick and died (314-315)
And what are the "joys brides hope to have"? This might be a reference to sex. Jeanie couldn't wait for her marriage, so she dawdled with the goblin men and ate their fruit. We now know that this was a big mistake.
In her gay prime (316)
"Gay" means happy and carefree, but during the period when Christina Rossetti was writing, it was commonly applied to prostitutes or women who were promiscuous. So this line could suggest that Jeanie had had sex before marriage.