My dog has a lump and is sleeping more. Could depression be the cause?

First of all, I'm so sorry for your loss. Saying goodbye to a friend is never easy, so I can understand Kalie's current depression. However, this type of loss and associated grief process won't cause a physical lump to occur. It's also difficult to determine if she's sleeping a bit more because of the lump or because of the loss of her buddy.

Given the prominence of the lump, conditions like an abscess (infection), granuloma, or benign or malignant skin masses must be considered. Unfortunately, there really isn't a way to differentiate between these conditions at home. Since it's difficult to get her in the car, perhaps you could find a mobile vet in your area who is able to come to your home to examine Kalie. They'll need to start with a full physical exam, and will likely perform a fine needle aspirate on the lump. This is a simple procedure where a needle is inserted into the lump to try to remove either fluid and/or cells for microscopic examination. Once the type of lump is determined, your vet will be able to advise you as to whether or not she needs something as simple as a course of antibiotics or even surgery. Wishing you and Kalie all the best!