I am so sorry to hear your sad news. My Jack Russell 'Cas' was into her 17th year when I had to make the terrible decision to end her suffering. She was everything to me, and more so when I lost my 14 year old son. I would be sitting alone in my home, deep in thought about my son, and she would wander into the room with one of her toys and drop it by my feet with eager anticipation of me throwing it for her to fetch. It was terrible taking her to the Vet's and signing the form ( it felt like a death warrant) to allow the Vet to end her suffering. That was nearly 6 years ago, and there's not a day when my wife and I don't mention her. I have photo's of her in my living room and a fantastic Pyrography 'drawing' that my very good friend, Mel b 3's wife Lin (also a very good friend) did for me.
Like my wife and I, you will feel sad and 'down' at times, but then smile when you recall the many things she did to make you laugh.