Is my cat goin thru depression?

Hey everyone its Gracie (: i have a goregous cat named Bandy. She is a 4 year old all white Maine Coon. Shes always happy, shes super lovable, never bites, and loves attention. Unfortunatley, we got rid of our other cat named Rain due to behavior. Brandy and Rain were practically sisters, but ever since we got rid of Rain, Brandy has not been the same since we got rid of her. I fed Brandy on Friday, and i went to check on her food today and there was barely anythingg eaten, then i went to clean her cat box today, ( i clean it every sunday ) there was NO cat duty in there except pee. Shes not as active as she usually is, she is an inside cat so she cant be sick, shes always sleeping, and she constantly needs love. We also got 2 new pups last week, 8 week old choco lab named Roxy, and 6 week old german shepard Eike ( Eye-ka ) she dont get along with dogs very well, and her symptons got worse. Is Brandy goin thru a depression stage?