I am unsure if you can change your screen name. You may want to go the easy route and make a new account if you can't find the answer.
It's unfortunate you were unable to keep Riley. Our pup Ninja had demodectic mange...and after one vet visit, $20 for medication and one bath she was fine and has never had the problem again (and most likely never will).
Best wishes with your new pup, hope all is well.
Kiba - German Shepherd/Border Collie Mix 10/2008
Scout - Basenji/Pitbull Mix 10/29/2009
Ninja - GSD 3/4/2011
Sino - German Shepherd/Blue Lacy Mix - RIP