I think it was OK for the therapist to call you (a little iffy---depends on your position at work---if you are Beth's t. for instance...could be fine...) and you responded appropriately. If you are not her t./pdoc; you may want to discuss this with a supervisor before moving forward.
My thought though would be that Kim's t. should be working with Kim on her telling Beth how she is feeling vs trying to find out if the discharge can be postponed ---
Kim needs to talk to Beth. That is my foremost thought. Beth needs to know what she has and does not have for a support network; and she needs to know the truth in order to be successful on discharge.