There’s a reason this has been punted as a beach-read, and I can see why it’s sold so well. It presses all the right buttons, and the prose style is closer to your common or garden woman-in-danger tropey psychological thriller than literary. That’s not a bad thing at all as literary style is often annoying and wanky, but it does mean that the book aquaplanes over the inner world of characters rather going any deeper. It’s quite happy with the therapy speak explanation - exactly what the main character’s audience is getting from this is constricted to her snarky comments about them, rather than pushing into anything deeper, or even wider. It’s a limitation of having a superficial first person narrator.
It sticks to the convention of a last act twist too, though it’s been one of the candidates for the ending right from the start, and I didn’t really buy it.