Can Alzheimer's Disease Coexist With Good Reflexes?
Not enough info to say that.
Detailed Answer:
I read your question carefully and I understand your concern.
Alzheimer's disease involves a decline in higher mental functions in particular memory followed by language, judgement, behavior etc. Reflex movements like catching a ball do not represent any important indication on that regard, do not involve these functions. So it is hard to judge if you do not provide any information about her symptoms, manner of onset, their evolution in time, other tests she's had like blood and imaging tests.
If the diagnosis was made based only on that questionnaire you mention then naturally it is not enough. That questionnaire indicates a loss in mental functions and the most affected areas, but that doesn't make the diagnosis of Alzheimer's. Alzheimer's is the most common cause, but there may be others like stroke, tumors, low thyroid function, vitamin B12 deficiency etc. it is for that reason that some blood tests and brain imaging is done in the initial evaluation, I can't imagine the diagnosis was made only through that quiz.
I remain at your disposal for other questions, but possibly with some more of the details of her history which I mentioned above.