@Howdoyoudoit31 Why is the OP being U? I hate the way some people just type YABU on AIBU threads, without saying why, very lazy. As if there couldn't possibly be another way of looking at it, as well, when that's very rarely the case.
As the owner of 4 cats who bring dead mice into the house regularly, I confess I don't get the upset about mice being killed, so my immediate reaction is to say she's BU.
However, the OP admits that she is over-sensitive and that the mice problem needed dealing with. OTOH, she had said to her DH that she didn't want to involve pest control as she wanted to find a humane way of dealing with the problem.
Mouse traps can be effective, though obviously more time-consuming than calling in pest control. (And I do understand the point about mouse traps not necessarily being completely humane. There probably isn't a way of dealing with a mouse problem that's entirely humane.)
My MIL had a problem with mice in her house and she did use traps, and blocked off the entry points the mice were coming in through. It was a hard process and we kept hearing about the mice, but the problem has now been resolved.
YANBU to be upset with your DH for going behind your back, OP. That would annoy me, too, especially if it was an issue I felt strongly about.