My 1st therapist as a young adult also did some of this with me. Although losing her was painful, I felt like giving me some light in all the darkness in my life was still worth it. Perhaps it's different because she got sick and died, she didn't voluntarily abandon me. I felt able to take the good I received with me through life.

My current therapist at least is clear on that we aren't fixing the past or anything. She is clear that I need to grieve my past and accept I will never have a real mother. She doesn't want to be my replacement mom or something or to have me think of her that way. However there are basic things that happen in a healthy parent child relationship that play huge roles in the formation of a healthy positive sense of self. Touch, acceptance and validation of needs, responsiveness to physical and emotional pain, mutual joy--- these things form the basis of core self worth. If you didn't experience significant abuse and neglect in early childhood you may not be able to understand what life is like when you didn't get any of those things or how much it helps to be taught that those strong primal desires for love and touch and approval are normal for some one who did not get them. I dont need to redo my childhood because I am an adust with adult thinking and insight. But I do need a place where I can learn to not be constantly ashamed of who I am and part of that is experiencing some of that validation, comfort and love.

It might depend what you mean by "reparenting". I think there is maybe more than one kind of "reparenting" therapy. For my T, I am expected to be a functional independent adult who also has a very needy small child inside myself. I think if she thought it would destabilize me my T would never have gone there. But for me the deep inner pain and wounds and need was constantly destabilizing and since we gave the child part of me room to exist I am much more stable.

True if she rejected me right now it would be awful but my therapy has changed my view of MYSELF just as that love in early childhood shapes a small child's view of themselves. she has been very slow and careful with it. I also don't get anything I am not able tof ask for. So my T wasn't all "i think your inner child needs love". She waited until I was strong enough and secure enough in our relationship to say " there is this very child like part of me with very powerful needs and I need help to manage that. These are things I think might help. Can we do x, y or z?"
Which i think is very different therapeutically from a T swooping in to "rescue" someone which often ends in disaster....