You don't need to worry... just be proactive in getting her the medical attention she needs. As for nothing being wrong... that is basically how they diagnose dementia. They look at the symptoms, rule out everything else, watch the progression, and then diagnose.
With Dad, he has cardiovascular problems for years. Three heart attacks, 5 bypasses, stints all over and they last stint was in a bypass. He also had PAD. If the blood is not getting to the legs then there is probably limited flow everywhere... including the brain. He had cognitive decline but it didn't follow the Alzheimer's pattern. That lead to his Vascular Dementia diagnosis.
Mom on the other hand had a perfect cardiovascular system (no kidding her heart cath was basically clean) and no other medical problems, taking no medication. She does have a strong family history of Alzheimer. So her symptoms lead to the dementia consistent with Alzheimer's diagnosis.
There is no test that can be done to diagnose dementia at this point. There are cognitive test that can pinpoint the cognitive decline but nothing that can tell you why. It's such a dark area in medical diagnosis.
Yep, you are now the one in charge of medical appointments. Try to consolidate as much as possible and find one good physician to be her general physician if you don't have one. You definitely need a clearing house for all that is going on with her. May I ask what her other medical issues are?
Hang in there. Not knowing what is going on is difficult but hopefully you will get what you need to explain what you are seeing
At least when you know you will be able to formulate a plan!