Big issues are being raised here. First off, if the 80 year old can't do her job, she should retire. Why do other people need to pitch in to help her? If she is getting a paycheck, she should be doing her job. If it is too much for her, perhaps there is something else there that she could do? We have an older woman (70's) at work, and she really needs to retire as she is not performing to the job standard. It is getting to be a safety issue. She has qualified for a pension, but doesn't want the decrease in her income, but she can't do the job she was hired for, even with accommodations.
Second - health issues should not be shared among co-workers. The supervisor should have made arrangements for the accommodations and that should be it. And since there is a file clerk (80 years old though) it seems there is a person who should be doing the filing as it is her responsibility.
Third - verbal abuse should not be tolerated in the workplace. Go to the supervisor, report what this woman said and did, and how she threatened you. Since you are disabled with accommodations, you are in a protected class of workers and she is in big trouble.