Three short lines, and they hold a quiet, difficult scene. Someone is dying, and the poem describes this as being "busy" with it, as if dying were a task she has to get on with. That choice of word is odd and a little tender. It makes death sound like something that takes effort and attention, almost like work.
Meanwhile, inside her mind there is a haze, "green and pretty." We can't be sure what that means, but it suggests confusion or fading awareness, and the poem refuses to treat it as frightening. Green suggests gardens, leaves, living things, so the haze feels soft and even beautiful.
The speaker seems to be watching from outside, unable to know what she sees. There's sadness in that distance, but also a kind of calm, perhaps relief that her last thoughts might be peaceful. The mood is hushed, gentle, and quietly sorrowful.