She won't change. You are in her house, so she is power. You won't change her. The only possibility I see is the way out. Finding another place. that's on the long term.
On the short term, try protecting your personal space and spending less time with her in the house, keeping your social life really active, taking off with your son for the week end, etc.
Another thing which can shift the balance of power is making sure you pay half of the bills while you are there.
Relationships with in laws are very tricky and it takes lots of good will on both sides to make it work.
I would check possible options for moving out as soon as possible.