Thank you guys for the condolences and well wishes.
At the lowest point in my life 14 years ago, this hyper, untrained, dominant puppy came under my care. My mom had rescued her from the pound, where she had already been returned once before, and my mom couldn't handle her either. So I took over. My dog and I worked through our shared difficult circumstances together by putting in the work every day. We literally saved each other.
I'm at peace with the decision for us to part ways, but I've still shed more tears today than I have in all my years put together. It helps to read the kind comments I've received, and I thank you all for your understanding.