Hi, I'd like to help you with your question.
It sounds like a couple of possibilities. One, your sister has a physical problem that is causing her to act like this. Thyroid problems, hormonal imbalances, the beginnings of dementia are all possibilities. She definitely needs to see her doctor for a full exam. If she is unwilling to go to see her doctor, you may want to contact her doctor to let him/her know what is going on. They will probably not be able to share anything with you because of confidentiality, but you could certainly tell them what is going on. The doctor may also be able to provide you with an idea of what might be the problem from the symptoms you noted.
The other option is a mental health problem. Given her age, the chances that she would suddenly develop a mental health problem is rare. OCD, such as your father had, would have manifested itself throughout her life and you would see obsessions and compulsions with her behavior. She does not sound depressed at all and you did not mention alcohol use so those are ruled out as well. Mania, related to Bipolar disorder, is a possibility but she would have shown signs of it before the age of 69. What might be a possibility is she has had a diagnosis all along and did not share it with anyone. She might be developing other problems now and it is affecting her disorder and it is no longer under control.
The best options are seeing her doctor and getting a full mental health evaluation by a Master's level or Ph.D. level therapist. She could also see a psychiatrist.
Is there anyone she respects within her friends or other family members that could talk with her about getting help? Since you have tried and she refused, maybe someone else who she looks up to could speak with her, maybe a doctor at her job or other nurse. You should also keep trying to suggest she see her doctor, at least. You could also try to get several family members together and all of you talk to her at once. The pressure could help her change her mind.
I hope this has helped you,Kate
She might be using it that way. But unless she is abusing it, I don't think it would affect how she is acting now. Alcohol is a depressant so it should slow her down considerably. If she was drinking to the point of alcoholism or alcohol abuse, you would see the opposite behavior that you see now.