We all feel your pain.
Making sure a dear dog-friend end its suffering quickly may be the right thing to do, but doesn't make it easy to do though.
God Bless You for doing the right thing, and God Bless Heather for being the great companion she was. She'll be with fine company while she patiantly and happily long awaits the reunion. She'll understand when you take your time - dogs are understanding about that and many other things.
Peace,