Here is a website that will help you find the answer and understand the poem as well...
http://www.sparknotes.com/poetry/hopkins/section4.rhtml
If you do not wish to visit the site I believe the answer is A.
Because she is mourning her own mortality, because man is mortal.
I believe it is a metaphor as falling from cloud 9 was usually used in older movies to express that they had fallen in love
It means having luster shinning which means his smile was shining
