You really are going to have to go back to the doc to sort this one out. Your mother's age makes treatment choices complex, i.e. some of the helping drugs that might be used, like the Anticholinergics, are very hard on the senior set, yet the right one closely monitored could provide relief.

The tightness of the throat can be a Parkinson's symptom, but it can also be a PD symptom that is aggravated by her environment. The throat acting up in the evening may be from fatigue or as the house cools and the furnace runs more the air gets dry. Forced air furnaces blow dust around no matter how spotless we are. So air quality, PD and fatigue can act on the throat. A humidifier or vaporizer in the bedroom can help. A window open a crack for some fresh air may help. With the medications you mentioned be really careful as many cold meds are out. They are relatively new drugs to me.

Remeron is an antidepressant and can take one to several weeks before you mom would notice depression lifting. Zelapar is a drug that helps Dopamine work better, and it is not to be taking with a number of cold medications hence the check with your doctor suggestion. Lastly, if she has mucous staying stuck it would be useful to insure she doesn’t have a throat infection - sometimes they are stubborn and just don’t go away unless treated. So in summary:

Anticholinergics – for difficulty swallowing, careful with elderly
Air quality and humidity - check
No cold meds or antihistamines without doctor b/c of medication interactions
Throat infection – check

As always suggestions only – seek medical help.
Regards, Guy