We say: Trust your instincts. When you get the feeling that your help is needed with aging parents, pay attention! Always! It’s best for you to not argue with her about her memory but do continue to pay attention to her behaviors. It’s preferable and more useful to talk with her physician and share your concerns.
Your telling the doctor about your observations of her symptoms may actually alert your Mom’s doctor to her condition as people with early Alzheimer’s are notorious at concealing their condition. Trust yourself and if you’re already beginning to have a concern, it’s probably already time to step in by learning more.