Gena, I do not know how you keep your cool. I would just combust!
As much as I absolutely think she needs to hear what you (as always) said so eloquently . . . I would be a little fearful of retaliation against your DS via her son. I would not normally worry about that, but this is NOT a normal woman and not a normal situation.
Are the aftercare teachers skilled/motivated enough that you could ask them to just keep on repeating to that little boy some of the catch phrases you wrote - - all kids are special, we are ALL here to learn from each other, etc? That little boy needs some counter-messages. For his own good.
ds 2007
dd 2010
baby dd 2014