Should I let my dementia riddled grandmother eat cereal and cheese?

My grandma doesn’t like most food but one of the things she still can tolerate is this frosted flake like cereal. I came home a while ago to find my grandma was eating this cereal with a shredded cheddar blend instead of milk. She said it was fine so I left her to it and my mom got mad at me. She’s very forgetful so this stuff kinda happens but the two things alone r at least a little nutritious so if she was enjoying it should we just let these kinda things be?