gzabetas -

"If you continue to bad mouth me, I will no longer help you with tasks like your resume or internet." Set some boundaries.

For your son, enjoy the extra time you get with him. She's dismissive? Hey, it just validates that she is not a good person to be with.

She sounds awful, whether or not people recognize her bad-mouthing. Don't play her game, be consistent, rise above. Stop saving the day.