So this is what the agent said:
"thanks so much for sending this new version. There is a lot of potential here and I am going to pass, albeit reluctantly. Climate change and apocalyptic or dystopian themed novels are difficult to place, although a further narrative layered on top creates interest. I sense that underneath the main narrative, this is a story is of grief? The loss of their mom; this is what moved me.
I know you have interest elsewhere and I am sorry to let this go.
If you write anything further and have not yet found representation, please stay in touch."
Having just watched 28 Days Later and googled 'Apocalypse YA Novels' my mind has started to go numb as soon as I hear the words: 'something just wiped out civilization'... so I guess I see her point. Sobs.