Mom's imagination is slipping away

My mom is 81 years old and has Parkinson's. She has not displayed signs of dementia yet but I'm starting to wonder. I noticed that she no longer does any creative activities and doesn't seem interested in watching movies unless it's an old western or something that she's very familiar with. On Easter we had my adult children over and everyone decorated sugar cookies and she chose to just watch. She likes to help me around the house and in the garden but she doesn't seem to take part in offering ideas like what flowers to plant or how to decorate something. Could these be early signs of dementia? She likes to do puzzles, but of course that's a very concrete tactile thing and does not require imagination. When I try to encourage her she very quickly loses interest and just wants to watch me. Perhaps it's depression, but I fear that I'll look back and recognize these were the early signs of dementia.