Hi Lynn,
First of all -- stop beating yourself up. Everyone handles trauma differently and by reaching out the way you have it’s obvious that you care very much and are feeling the anguish that comes with situations out of our control. Just because your Mother’s body is betraying her she’s still the person you know and love. You might try going to a Parkinson’s Disease support group with a friend – there are pros and cons to this as many people are elderly and further into their PD journey and that might throw you, but I found their strength of spirit and the “this is not going to beat me attitude” encouraging. Also, you meet many spouses, friends and siblings of people with PD. At meetings you’ll find literature, pamphlets and less daunting material. Another time you may go to one of these meetings with your parents.
My guess is that you are frightened and if that is the case push yourself to talk to your Mother and tell her so. When it’s time to cry, you’ll cry. You’ll never regret having made this effort and I suspect you will feel much lighter.

On the purely practical side of things, I agree with the others – some adjustment of medication may help her greatly. In the beginning I had that left sided drag to such a degree that I was wearing out my socks, or I should say one sock through the heal. The doc put me on Requip, an agonist, which stimulates, for lack of a better description, the Dopamine producing cells that are responsible for smooth muscle control. When she communicates these symptoms to her neurologist and adjustments are made you’ll likely see improvement. She may even put some healthy weight back on. Tremor and drag have a way of weighing you down and wearing you out...

Also, and I mean this in the kindest way, don’t fool yourself. Your parents know that you are upset. I really encourage you to talk. If it’s not something you are used to doing take some of these responses you are getting and read them or share them at the next Sunday dinner. You only ever get one Mum. I wish you the best and greater peace of mind.
Regards, Guy