Negotiating Contract

This has been on my mind for a couple days now and I think it’s best if I get some outside perspective. Here are some circumstances and thoughts:
– I am a contractor.
– I was offered a contract from client and my mentor is helping me negotiate.
– I wrote my notes/concerns in an email and the mentor communicated them with the client.
– I asked mentor to please forward me what they sent to client, she did so.
– There were a few things that were changed, worded differently, okay things I did not request, but left it.
– After not hearing back from client i asked mentor for update on contract.
– She forwarded response from client and included was text that she was requesting “$400/month cut to her agency” which comes off of my salary
– This is were the brain starts to go to work creating stories:
– I understand she needs to take a cut, it was communicated before hand but why was it taken out of the original email? Why didn’t she want me to see?
– I would have been open to the conversation, but it all seems secretive.
– I AM grateful for the contract and opportunity but I am acting like a victim.
– I feel betrayed and mislead, because of the thoughts I am thinking about the way she is doing business.
– I must deserve this is some way. What is the lesson here?
– Is it worth approaching the mentor about the request that wasn’t in the first email? What would my reason be? To let her know that I know and I don’t agree with those actions. J would have rather had the conversation with her on her cut beforehand? Is this who I want to be?
There are so many models I can create based on the above TDL. This is my first contract negotiation (in this scenario with client and mentor). My question is this: where should I start? With what thought should I start model work? Thank you for taking the time to read this lengthy message. I truly appreciate it. 🙏🏻