Oh Gosh, I am sorry you are going through this. I know how difficult therapy retirements can be--both for the client *and* the therapist. Your therapist has likely never retired before and is navigating this new space too. it is a difficult time for both of you.
<<She said "so it's me you want?". I felt so ashamed. She asked me what I need her for if I don't need a therapist. I mumbled something and then said I didn't want to talk about it, couldn't cope and left.>>
I don't think you should feel ashamed of wanting her. Why wouldn't you? This is another human being that you've had a relationship with for a decade! It's normal to want to continue it, if possible. I don't think you should feel ashamed of dependent-type feelings you have towards another person that you love. Those are completely normal and human. And of course therapists are not interchangeable.
Her question about what you "need" her for may have been sincere but it sounds very badly phrased. Perhaps she is trying to understand what her role will be going forward. I think you could reasonably say, "I don't feel I need a regular therapist, but we have a long history together and I'd like to know you were there occasionally if I needed a session to talk about an issue that comes up." I even think you could say, "I hoped you would miss me and would want to be in touch and it's hurtful that you don't seem to feel that way." The question is, what will your relationship be if she is "retired' from being a therapist.
I think she's handled this badly but, as I said, it's a new experience for her too, to be retiring. If it were me I'd just go in and admit everything you feel--admit that you felt ashamed, admit that yes, it is her you want, and talk about how the ambiguity is hard for you. Maybe it would be better for you both to say that the therapy relationship is basically ending and that she will be available for the occasional card or call just to stay "in touch" but for therapy you need to have a local, new therapist. I know how hard it is, though, to even think about someone new. I'm sorry you're going through this. Honestly it sounds to me like your therapist has some of her own stuff going on there.