You say you have a history of depression and asked for some personal help. Do you have health insurance at work? Most companies have some sort of EAP program where you can get assistance. I would explore that option.
Not sure how long you've had her, but many people consider and treat their pets as first class family members. Losing one like this can be no less than losing a child to some.
Sounds like you got some solid advice above. Best wishes.
We humans are by no means perfect, we miss stuff and make mistakes all the time! No need to beat up yourself with guilt over it. Most of us here have had losses, some more than one, over the years of keeping animals. We keep them because we love them, and that is the best thing we can do for them! We all very much hope you get her back and that you will stay here and keep us updated.