Is there a test that can measure if someone is lacking Acetylcholine?

My 83-year old mom has had a sudden change in her short term memory. Her MRI is clean, vitamin D is at healthy levels, no UTI and she isn't on any prescription medication. Her doctor cannot find any clinical reason for her memory loss and does not see any signs of Alzheimers. Her doctor suggested Aricept because it helps to fight the loss of Acetylcholine which is a deficiency that is commonly found in Alzheimers patients. Is there a way for my mom to build up the presennce of this enzyme naturally, rather than take an rx that has many side effects and only slows the depletion of the enzyme, Acetylcholine?