Orangefatcat, I am so sorry to hear about your stressful day and I am sending you a ciber hug as I feel that is what you need most right now.
You obviously love your mom very much and it is painful to see her looking ill and frail. The WTS is so cruel the way it encourages its elderly folk to cut themselves off from the people who love and care for them most, just because they do not share their religious convictions. If only your mother could see that this does NOT make you 'Satan' or any less of a loving, caring daughter. It would be laughable if it wasn't so tragic.
Regarding your son, as the song goes "you always hurt the ones you love, the ones you shouldn't hurt at all", which happens to all of us when we are upset. Go give your son a big hug and tell him how much you love him and how sorry you are. Explain you were just upset and not thinking straight when you said the hurtful thing to him which you obviously did not mean. I am sure it will work out OK.
Just carry on visiting your mom, showing her love and affection as you are doing. This proves what a warm, kind hearted person you are which I am sure deep down inside she realises. She is only saying these cruel things to you because she has been indoctrinated by the WTS, and they are not really her own thoughts and feelings. I have learned from experience it is no use arguing with them when they are in this mindset, just try to ignore it and keep to discussing light hearted issues.
The main thing is to make sure you keep in regular contact with your mom so that you are available to help her when she needs you, as I doubt very much if she will get the same level of care and attention from the 'loving' congregation.
Take care orangefatcat