WELL as a married couple for 16years neither of us would allow our family members to behave this way towards the other. We have enough love & respect in our marriage that we don't let people barge into our homes or their animals to kill or terrorize our pets/livestock.
Marriage is not always about biting your tongue just because it has something to do with conflict with the in-laws. When you marry someone you leave that family and cleave unto your spouse to become one you don't allow the in-laws to dictate your stress level or your own home.
The question was asking what you could do to change the mother but when we give advice you don't like it. I don't mean that to sound rude but seriously the only way you're going to stop her from doing these things is to speak up and explain to her what's going on and take the key back that's all you can do at this point, because it sounds like she's been catered to & allowed to act whatever way she wants towards you.
There doesn't seem to be any sort of boundaries whatsoever.
There can still be love with extended family and still have boundaries in your own home.