best friend lost someone she really cared about

I am sorry to hear that your best friend lost her dog as I know it must be very hard on her. It was very hard on me as well when me and my parents lost our dog when I was younger. Pets are family members so it is just as hard as losing a parent or brother or sister. She just needs some time to mourn. I think she will be okay after some time has passed. Just continue to be her friend and talk to her and give her a hug when she wants or needs it. Eventually she will realize that her pet is in a good place and will always be a part of her.