Yes, her egg, if it is a hen, will be 50/50 that it will be green. (Since either dad is a brown layer breed, the pullet will lay green IF she got the blue gene). It might even be a slightly darker green if it beefed up the brown wash...but chances are just a light green.
Hopefully it is a pullet.
If not, the rooster should have a 50/50 of having the blue gene, statistically, and you can keep the blue gene alive by breeding him. That of course takes a bit of time to know if he has that as you have to wait for his daughter to grow up to see what she lays, and you have to do enough daughters to overcome the statistical odds (you flip a quarter enough times, 50/50 heads/tails does work out eventually but you may have 10 tails at first, etc.)
If the mother had a pea comb, following the pea comb can be helpful as the blue gene is closely connected to the pea comb allele and usually the pea comb and blue gene pass together.
Sorry to hear of your hen loss.
LofMc