OP, you need to save yourself first. If you have the surplus energy and inclination to help her, then you are a Saint and a great friend.
Bleeding on you is a better way to say it too, btw. I’ve read less kind people call it hatefully "being an ‘emotional vampire’ ".
I agree with others that you’re an awesome person, and you can’t fix her. She’s not just having a bad day/week/month, she needs professional help. Can you try and persuade her to see a different therapist, or talk to her doctors about different medication? The one(s) she’s taking now are clearly not working well anymore, if they ever did.
I also think that, until that gets sorted, having a cut-off point where after X time you no longer take her calls might be a good idea. Tell her that you and your husband are exhausted at the moment and need to concentrate on getting some more sleep for a while so you can deal with your own problems. If your mutual friends have had similar struggles with managing her moods, how have they dealt with it? Maybe follow their example?
Kate has professionals that she can talk to - you don’t have to do their job for them. Encourage her to contact them, even late at night - there must be emergency services she can use, people who have training to deal with this kind of thing. You’re doing your best, you and your husband, but you have more immediate worries and you shouldn’t feel bad about focusing on your own issues. Would it help to have a standard response of something like “Kate, you know I care about you, but you need to talk to someone who can help you properly. Why don’t you call [crisis helpline/therapists emergencynumber/someone who isn’t you] and tell them what you’re feeling right now?” the first time, then don’t answer any later calls from her. You’re not responsible for keeping her alive, she is. And her doctors are. But you’re not - you’re her friend, and you care about her, but you have your own life you need to lead too.
I agree that a time cut-off point is a great step.
I suspect that the explanation offered, while fine in most any other circumstance, would backfire in this particular case. Based on the description of her behavior, “we’re exhausted” would be understood as “you’re not worth our energy,” “at the moment” would be understood as “this will only last a couple of days,” and “so we can deal with our own problems” would be understood as “your problems aren’t important.”
You’ll have to give some sort of explanation, but this is a case where less is more. The “we need to get more sleep/get to bed earlier” approach should work - as long as you don’t give her an “in” to argue with you. It’s really a good circular argument. You have to get to bed earlier because you need more sleep, and you need more sleep so you’re going to bed earlier.
Then tell her you can’t talk during the day because of work/school/golf and keep adding restrictions until all she has left is a window between 8:02 and 8:04 PM. It’s really too bad that you end up stuck in the bathroom with explosive gastrointestinal distress between 8:01 and 8:05 every day…
Call me names if you want but my wife has had some friends do this with her and I strongly suggested, maybe even made, her drop them.
Why? They were really bringing my wife down and she didnt need it besides these friends were refusing help. My wife isnt a doormat. Afterwards she was actually glad I pushed her to drop them. She really wanted to anyways and just need an excuse.
She sounds like one of the helpless of the world. I avoid these people like the plague.
They don’t bleed on you, they suck all the blood out of you. They enjoy doing it. Everything is about them, them, them. They are the only people in their world who have problems. They rest of us are all living la-la wonderland lives.
Drop her, and let her find some other victim.
Yeah, people who only think of themselves are awful, right?
So what is her goal at this point? If she’s (objectively) super attractive with a very high IQ and apparently has one or more advanced degree(s) what is the specific trigger for her unhappiness? Is she employed? Does she go out with friends? What does she view as the main central dysfunction of her day to day life that cascades into these marathon phone sessions?
There probably isn’t one. Or there could be many. Brain chemistry in a depressed person doesn’t work like you think it works. He main central dysfunction of her day to day life is brain chemistry that blows everything out of proportion, throwing her into a spiral of despair, fueling failure, creating more bad feelings that get blown out of proportion, intesifying the spiral of despair, fueling failure - until you are failing at things like not shitting yourself because you can’t make it to the bathroom (my personal lowpoint) - the triggering event was, I think, breaking a coffee mug I liked.