You might want to check with her doctor. It could be the result of a GERD, hiatal hernia or other swallowing difficulty that can be treated. Mom does have a hiatal hernia with GERD. When it is irritated she does occassionally choke on her pills and meals. She was put on puree/soft foods for a while and her pills were crushed. After a while the Hiatal Hernia healed to the point that she was eating again. Dry foods such as bread are especially rough on a hiatal hernia. Mom repeatedly choked on sandwiches but could eat the chicken salad, pimento cheese, or egg salad that was in them with no problem. Carbonated drinks were a trigger as well. And antiacid helps.
Otherwise it could be just as Caring said. The brain does forget how to tell the throat to swallow but this is usually in the laster stages of ALZ. They are usually able to handle thickened liquids for a while. Medication is available in liquid form or patches and some can be crushed and added to applesauce of pudding.
It's worth giving the thickened liquid or puree diet a try and finding medication alternatives that don't involve swallowing pills. Add a nutritional supplement a couple of times a day if she will drink it. You an also add milk shakes and other soft high calorie foods. These will help maintain her wait if she is still processing foods.
It is frustrating when Mom is losing weight and unable to eat due to choking. Good luck with finding the correct answers to your Mom's problem. My first step would te talking to her doctor