Why won't me dog eat? is she depressed?

Recently about a month ago my dog Diamond died from spleen cancer he was 13 years old. My other dog Roxy who we adopted when she was a puppy has had him with her, her whole life. after he died Roxy didnt really seem to react since he had to be put down at the vet. abbout 5 days later we realized she doesnt eat. We tried switching her dog food and she still wont eat. she will eat a couple bites here and there but never her full meal. this has been going on for a couple weeks. We have been giving her all the love she needs and been taking her with us and stuff. I dont know what else to do. Can someone help me out?