Tad, I'm very sorry to hear that your mother is suffering quite a bit. Is hospice visiting w/her? If so, someone needs to advise them that she is suffering a bit more and they can adjust her pain meds.
As for your xw, once you stated your point w/her, you should have left it alone, no matter how many texts she sent. Your son is old enough to handle his own battles and all he had to do was allow the message to go to voice mail and deal w/the messages later by deleting them if he didn't want to listen to them. Tad, there comes a time when your children have to stand on their own two feet and since his mother is the rose w/the thorns right now, he needs to tell her that whatever is going on is between you and her.
Your xw is still looking for ways to take pot shots at you. This is not the time for that kind of stuff, i.e., w/your mother in the shape she's in. Stop taking her bait and when you don't fuel your xw's fire, it will die out.
Again, state your point when you deal w/her and then walk away or cut the conversation short. There is no need to continue defending yourself. You know you weren't getting the money...so let her investigate her own deductions and figure things out.
I am keeping your mother in my thoughts and prayers. Keep your focus on what is important right now...your mother.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.