she bounced back and forth about calling off the divorce, she can do the marriage, to why can't I just let her go, tell her what I want and she will follow, to she is scared b/c I might seek full custody, she will have her attorney make the needed changes, I mean she was all over the place

IMO F4W, I dont see these comments as being all over the place. In each and every comment, you can see her either acqueising to you, or asking your for leadership. Her emotions have her so overwrought that she is communicating directly with you, with barely a hint of womanese. This is very positive.

Now this doesnt mean I want you to go shout, demand or even tell her to stop the divorce. Your actions and responses to her were excellent. Seriously. I had to do the snoopy dance. BF--->

A lot of those comments took either big brass ones or indifferent detachment, and you obviously are not detached.

Im going to guess that you are thinking... how can the statement "why can't I just let her go," be positive?

She is seeking validation in this comment. In your pain, and fear of loss, lack of confidance, you are misinterpreting her intent. She has treated you abominable and she knows it. She doesnt think she deserves your love. This is one reason you need to lay off the ILY. She cant let you love her, and those comments and behaviors give her something to resist. This is the reason your telling her she isnt nice and you dont like her very much right now, is positive. It meshes with her inner voice and lets her know she has things she needs to work on. Its the opposite of supplicating. Its the truth, and its congruent. she doesnt have to fear a hidden agenda down the road, (backlash, anger, cruelty, fake love) when she sees you coming from your place of honesty.

All while you are standing there steadfast and not jumping up and down the emotional ladder with her. Women are so attracted to that. This is just another test.

So a couple ideas.
Do you know the concept of imagary? its used in sports alot, but it works in all things.
Continue to be certain of what you want. See it. Dont let anything Shake your vision of what you want to be.
if or when she says blah blah let me go.blah blah. try something like ' Im not holding you here. Im glad that you are, but You are here,..... because you want to be.' This comment is confidant, and reassuring. ignore all negative responses or cruel words, if.... .


Try to eliminate the ---'if you want'... or... 'you know, you dont have tooo'.... etc. It comes across supplicating. She knows she doesnt have to do anything. It doesnt have to be said. You arent forcing or demanding anything. Just being certain, confidant, and headed to where you want to be.

Think of other ways to communicate that you are certain she loves you and confidant she wants a good marriage with you. Every time you fight she practically begs you to lead.
sooo.
lead. with baby steps. Little things. day to day stuff.
no demands. if and when she chooses not to follow, shrug it off.









So my sister writes an email to my STBXW and tries to get her to consider joint custody
This is the second time OP has gotten involved in your affairs. I dont see any benefit. Unless you do, get these OP under control, where it comes to YOUR marriage. I know your sister saw you in pain. Its not her problem to fix though.