I'm so sorry that your going thru this.
I and many others on here know what your feeling, your not alone. It is such a very, very hard decision to make. My sister told me these things after I had to have my/my mom's dauxie put to sleep; That if GiGi could talk, she would say, Thank You for taking away her pain and my sister also told me; it's the Circle of Life.
Sending you hugs and prayers.