The idea that you can't go against your core, if that is even a thing, obviously can't apply to a DID
system. Each alter can have a core them, but your body doesn't have a core, it has a system.
I agree,
all people have conflicting thoughts and desires in their heads. You and I seem very much in the same place with that. I am also always wondering now whether a conflicting desire is alters not agreeing or just standard brain function: it makes sense to want something sweet, but also know it might not be the best thing for you, so you have typical conflicting desires. I am finding that a challenge too. LKinney tried in the summer just never saying no to anything, to give in to any desires just to make it easier, but that doesn't work because individuals still have conflicting desires: "I want pizza."/"I want to eat better to control my blood pressure." (my conflict last night - pizza won.

)
I am trying to stop and listen when I have a conflict now. Do I actually HEAR another alter talking to me? So the other night I did as Punky clearly stated what she wanted. It was not what I wanted, but since it was the first time I am aware of her showing up, and she seems very young, I decided to meet her needs over mine and the body (she didn't make a healthy eating choice either) for this time. At some point though, we're going to have to learn to do better for our body because of our blood pressure problem, but that was not a fight I want to have at this stage of our alters all starting to assert themselves.
Alters act based on THEIR needs. Most of us are horribly scarred and ashamed of things Black Tiger has done. Black Tiger has hurt those we cared for most in the world. Black Tiger has no shame or guilt for her actions, she is a tiger, an animal alter, and acted to protect the system. Jessica, however, has to live with the guilt of Black Tiger's actions. Believe me, they are very much in direct opposition to each other. BT's actions didn't actually help the system, she was wrong, but she reacted with animal instinct.
Your T is not helping you by saying you are the "real" you. I know I am new to this too, but I understand, everyone in the system is equal, and this is very clear to me because LKinney thought she was the "real" one and the rest of us were not. She tried to control and suppress us all our lives. That is wrong. And eventually the accounts came due; we were not going to let her forever, and we have forced our way forward. LKinney still doesn't want to deal with us, so she retreated back and shut the door making it very hard for
me to speak to the others, but I know and accept we're all here and all equals.
Your T needs to do research before your T speaks to you about any of this again. I would suggest you ask your T what DID research she's done. What has she read, who as she consulted, what EXPERT advice on DID has she sought out. If she is not doing anything to educate herself SPECIFICALLY on DID, then she is going to do harm, not good.
I wonder if she's approaching this from a PTSD point of view, where you can have emotional parts, but it's not the same as DID as DID develops in childhood. PTSD is not creating alters, but it's sort of walling off a trauma. How you treat that is not how you treat DID. DID is you never had a "core" personality to begin with because your baby ego states never developed into one personality to begin with. This is my understanding from what I have read so far.