Sorry for your loss. It's really tough when unexpected.
We had two bull terriers, a staffy and an English and they loved eachother. He died suddenly when he was 6 - and I'm afraid she was utterly distraught. She barely ate, and worst of all, she trembled all day, sporadically. It was horrible to see.
I had been told that it helps a dog to come to terms with the loss of its companion if you show it the body. Just before we buried him, we tried to take her down the garden but she refused. She wouldn't look. And the whole rest of her life, she never went in the bottom garden by choice, ever again.
This went on for weeks and in desperation, assuming it might even be woo, tried a herbal supplement from Herbaticus:
Wolle's 1874 (had to look it up it is so long ago I forgot its name)
www.herbaticus.co.uk/page6.html
I had seen it recommended on a dog forum. Truly expected it not to work but I was desperate. And... either it worked, or enough time had passed but anyway she stopped with the shakes and started eating normally again.
She was always a quiet, withdrawn, sweet little soul. We decided not to get another dog though as if it hadn't worked out it would have been disastrous. So we gave her all our attention. And she adjusted. But it took several months maybe even 6 months. She died last year aged 14.