OK. I'll take it from the top.
When Ms PITA and I go to see Boss about this project, the work we present will be a draft. We still have a way to go before it is finished. Boss will want to discuss the project, put in her two cents, and by the end of the meeting there will be many, many changes to the project.
During this discussion, I will bring up my ideas. That means: I will talk about them. (I won't be bringing a whole separate draft piece of the work and dropping it on Boss's desk and saying "This is what I did.") I will mention them more as if they've just come to me that moment. I can also steer the conversation a little in the directions I want it to go so that I get a chance to bring up my ideas.
In my experience, this is a very common way of doing business. You don't lay out all your cards on the table - unless it's a conscious part of your strategy.
Now, contrast that strategy with how I used to deal with Ms PITA: I would be "nice", generous and trusting. She and I would have meeting to talk about the work and I would share all my ideas with her, while her contributions were effectively nil. She and I would agree on the next steps to take regarding a piece of work, and then she would go off and do whatever she liked, not what we agreed, and not telling me about it until after. This usually took the form of her having an impromptu meeting with Boss about the work (which she would not bring me into or even tell me about until afterwards) during which she would discuss all the points I raised during my meeting with her. Of course, if I'm not there, I have no idea what she is telling Boss or what kind of impression she is giving Boss about my contribution, and I do not have the opportunity to address any misleading information. Ms PITA has done this sort of thing even AFTER I expressly told her that I want to be included in all meetings with Boss about our work and that I do not want her to speak on my behalf.
I'd have to be out of my mind to let this go on. This is how careers fall apart. Since I don't have the kind of boss who can handle hearing about this sort of conflict or doing anything about it, I have to find another way to protect myself.