I know exactly how you feel. I raised a black lab for Leader Dogs for the Blind and it's very hard to let them go.
When she graduates and you get the letter and a picture (I don't know exactly what PWAC does..) of the new team it's the best feeling you'll ever get.

Here's my girl, Abby, on the car ride to LDB headquarters in Troy, MI. Worst 11 hours of my life but what she's done has more than made up for it.