Recently my dog, Willow, has been very down lately. She keeps hiding in another room on her dog bed, she hasn't been as energetic even with her favorite toy, she rarely wags her tail, and she just, in general, seems sad. A few months ago we had to put down one of our other dogs (we currently have 2 dogs and 2 cats), Chelsea. Chelsea was the only one who ever played with Willow because all the animals we have right now hate each other except Willow loves everyone. We had been worried before when Chelsea was alive, how Willow might react when Chelsea passed since Chelsea was very old. Along with that, my dad and brother have been gone for about a week or so now. Willow is my dad's dog. My mom makes small jokes now and then about Willow having doggy depression, which however much I hope it is not true, may actually be. I have researched it, and I'm not sure. If she does have doggy depression I'm not sure what to do. I try to give her as much attention as possible, however, I have schoolwork all-day, every day. I've been planning on taking her for a walk tho, to see if it helps. I'm very concerned. If any of you can help or offer advice, it would be appreciated.
Edit-
I figured out that the dog bed she has been laying on (she has two in the room she's been hiding in) is the one we had our dog Chelsea lay on in our car when we went to put her down. She is likely reminded of Chelsea on that dog bed.