Ed raises a couple of valid concerns: depression and drying/tearing of the eyes.
It sounds to me like depression is a more likely cause. I would be very concerned about and aware of depression. Depression can be situational (divorce, death, dealing with Parkinson's) or it can be due to a chemical imbalance. Both are common with PD. The individual has no control over depression due to a chemical imbalance. However, there are a variety of meds that can help either cause. Meds are basically the only thing that can help if it's due to a chemical imbalance. Meds can also help if it's situational. Unfortunately, the Parkinson's 'situation' doesn't go away (unlike working through a death, divorce, etc).
Sometimes it can take awhile to get the right med and dosage in place. Hang in there because it can turn things around.
Your mother is fortunate to have an advocate like you taking such an active role in her care. I'd research depression, the causes (especially chemical imbalance) and the treatment alternatives. The right treatment can turn your mother's outlook and life around. I wouldn't settle for the explanation that your mother is an emotional person (my opinion).
Here's a link to a National Institute of Mental Health site about PD and depression: http://www.nimh.nih.gov/publicat/depparkinson.cfm Hope this helps.
Life is a dance. Don't sit it out. --- H. Jackson Brown