I always saw Karen as a parallel to Beth. Both are emotionally fragile, yet live in a world of denial by busying themselves with social activities (parties and tennis for Beth; drama club and school secretary for Karen). Both get uncomfortable when Conrad talks about the hospital and other uncomfortable memories. Both refuse to go to therapy
Beth has nothing to do with Karen, no more than the fact that most people don't seek the therapy they need (and all the rest) Karen stopped going because she thought she was alright; that is not refusal. Did Dr Berger say she "refused"? It's very common to stop going to the shrink when you feel better. I don't see Beth as emotionally fragile; narcissists are not fragile (nor veiled fragility)
Most people get uncomfortable when talking about things like the mental-hospital and suicide. I don't see the parallel, except that people need to find parallels and subtext to elevate the film and non-extent symbolism. If we didn't we wouldn't feel as perceptive,
Look look look real deep to find hidden meaning because it's highly-rated prolific film.