Personally, I think a lot of your frustration stems from your inability to deal with such manipulation.
The simple (example) response to such attempts at manipulation is "Mum, this is my news, I'll deliver it in the way I think appropriate"
Manipulative people often then try guilt trips eg "So it's inappropriate to listen to your mother" (etc)
The simple (example) response is "The delivery of this message is a significant event in my life - trust me to deliver it appropriately"
In each reply to her, you repeat the heart of the message (it's your message, it means a lot to you, you can judge what's appropriate etc)
As a note: The first few times a person changes and starts standing up for themselves, the manipulative person (particularly members of the family) try guilt trips, and if you keep standing up for yourself, they up the ante (because they can't understand what is going on - they aren't use to it - and upping the ante has always worked before. Manipulative people are creatures of habit when it comes to how
However, with continued (respectful) firmness, manipulative people usually stop, or tone their attempts right down. No where in such conversations do you need to get 'livid', nor threaten violence.
Your ease of upset / lack of emotional self control is one
of the significant reasons she is able to manipulate you - as manipulative people, if they can't get what they want out of you, still feel like they've had a partial win if they've upset you (unconcsiously they understand it is much easier to manipulate people who upset easily). Also, likely your anger, in her eyes, justifies her further attempts to control your wife, and to her 'you deserve it' .
Your lack of skills in dealing with such manipulation is the other significant reason.
As a note, these two aspects of a persons life are very common in victims of manipulative people. They are both aspects that can be changed, and improved, to reduce or eliminate attempts at manipulation.
You are able to make improvements to both of these aspects of your life. You can, if you put the work in, stop people from manipulating you...in every part of your life, for the rest of your life..