There’s no anti-gun message, she’s just obsessed. The ape that wanted a war wanted a war before he got a hold of any guns, he used the gun to start the war because they were (to that point) human weapons so when chief ape got shot all the other apes thinks humans did it. It’s a good movie, any message in it is against unreasoning hate and pro communication with supposed enemies.
Dang. No spoiler alert? LOL! I thought it might have at least had some Darwinian message. I guess some people can read something into anything.