How about celebrating that she lived and was loved and happy. Abbey sounds like she was such a little trooper, I don't think she would want you to be sad on her birthday. Maybe go for a walk at one of her favorite places, have cake, get some special treats for your other dogs. Release some balloons into the sky, laugh, have fun and remember the Abbey that enjoyed all those things.

Don't Grieve For Me
Don't grieve for me, for now I'm free; I'm following the path God laid for me.
I took His hand when I heard Him call; I turned my back and left it all.
I could not stay another day, to laugh, to love, to work or play.
Tasks left undone must stay that way; I found that place at the close of day.
If my parting has left a void, then fill it with remembered joy.
A friendship shared, a laugh, a kiss; Ah yes, these things, I too will miss.
Be not burdened with times of sorrow, I wish you the sunshine of tomorrow.
My life's been full, I savored much; good friends, good times, a loved one’s touch.
Perhaps my time seems all too brief; don't lengthen it now with undue grief.
Lift up your heart and share with me,
God wanted me now, He set me free.