I went through a slight depression about 6 years age. I lost interest and then I knew something wasn't right with me. I got a prescription of wellbutrin from my doctor and took it for 9 months and worked with a counsellor. I finally came around and all my favorite interests came back -- crochet, crafts, sewing and quilting. I never want to be "there" again. I am happy again. My patient husband was a great supporter. So, yes, depression can be a cause of your mom's loss of interest.