It's also obvious to me that she derives some perks from keeping herself from getting out of said spiral. Why else would she remain with a therapist that clearly has reached the end of the rope in how much she can help Zoe?
It happened to me, I started out with a therapist (Ericksonian Hypnosis) and it helped massively when I was having panic attacks that literally landed me in the ER, thinking I was having a heart attack. But after a year, I was better but I wasn't getting better-er, for lack of a better word haha. So I switched therapists, did CBT and that helped me move further along in my health journey. It doesn't mean I never ever get anxiety or anything anymore, I do, but now I have two different techniques/toolboxes. And I'm better than I am when I was just going to the same therapist.
She just stays with the same lady who clearly can't help her beyond what she's already done. To me, this says that at some level, Zoe is comfortable and obtaining perks from her attacks. Alfie probably pays more attention to her. People don't demand she be responsible and hard working. Etc.