Pets can suffer from mental illness :)

[Delta4Embassy]

One of my Mom's dogs had OCD. Whether it's fetch, or staring up at something placed out of reach she wants, or anything else, she gets focused on it and just doesn't let it go. Happened at Christmas dinner, exhausted me sister-in-law, my brother, andmyself playing fetch. Then when she wanted a pet gift for my brother's dogs she sat there staring up at the package for a few hours until we got so disturbed by the obsessive stare we picked her up while I went and hid the package

So yes Virginia, animals can suffer from mental illness.

 

[Kooshdakhaa]

Indeed. I have five dogs and six cats and some of them clearly have issues. Maybe not quite as bad as your mom's dog, but issues nonetheless, such as sucking on blankets (causing holes in them), constantly wanting to be petted, etc.