Welcome to the forum, we're definitely here to support you at this difficult time (well, I'm here to give/receive advice more than to validate - but other folks are great at validating!). You're absolutely right that "Eggshells" (and anything by Kreger/Eddy) while being heralded as "the" book, is actually quite light on solutions and should be seen more as a "gateway book" that leads you into more detailed books. They offer the bare-bones basics.
Unfortunately despite BPD's prominence, the actual literature on it falls into three categories; "survival stories typically written by BPD patients to tell you what it's like", "psychobabble that attempts to cold-read every person who might pick up a book on BPD so that flipping through the pages you think it applies specifically to you but it's actually light on information", and "useful". The third category is the most difficult to find by far.
So far as falling down the rabbithole of useful books, while avoiding the useless ones, I'd probably suggest "I Hate You, Don't Leave Me" by Straus and...Kreiss? It's two names like that. It's a little more detailed on all aspects. "Sometimes I Act Crazy" was less useful in my circumstance but still more useful than the memoirs. You'll find BPD book reviews by members of this site at
https://bpdfamily.com/message_board/index.php?board=33.0Ultimately if there's one or two aspects that need your attention most, it's best to let us know so we can offer more pointed advice.
I'm assuming based on a week's hospitalization that she just had her first major suicide scare? There's good news and bad news here; the bad news is that BPDs have one of the highest suicide rates in psychiatry, and the highest in personality disorders as I recall - but the good news is that's still only 10% so the odds are decidingly in favor of life - and a high number of those who do die appear to do so "accidentally" by miscalculating something (you might have noticed that in the middle of a fit BPDs are often not very competent). Don't keep a gun in the house, don't keep extra-strength drugs in the house, if she's got a prescription for something, just ask the pharmacist to put it in three bottles of ten-day supplies instead of one 30-day supply - they know why. Give her one bottle at a time to limit the efficacy of any overdose. I even advocate replacing any reference to potential overdoses with "non-harmful" drugs to put in their mind as I've found it invaluable. "Make sure it's been X hours before you take another Amoxicillin antibiotic for your cough, they can be really dangerous if you take too many", etc. Those are the two most common BPD parasuicidal/suicidal techniques, but I think between the various families represented here we've probably seen just about everything.
It's often possible to "segue" a pwBPD's self-harm from one method to another, less dangerous, method - although probably best if you are able to do it without mentioning it's because it's less dangerous. Plucking out one's hair or burning oneself with cigarettes/lighters is not healthy...but it's also not going to accidentally lead to death.
On transitioning, keep your expectations low is key - many BPDs are going to be living at home quite a while past 18; those who do move out often move back in when a relationship crashes or they run out of money, etc. It's easy for them to find a relationship but remarkably difficult for one to last. God's given us extra challenges because He things so highly of our abilities to be fonts of compassion apparently. That said, there's a light at the end of the tunnel, the majority of BPDs do improve through their 20s and self-harm/suicide is typically very low (comparatively) by their 30s when they just retain the emotional disturbance.
I have spent a substantial portion of my life in libraries/archives/universities, so if you come across an academic article online that you can't access - send me a Private Message. Psychiatric journals are my preferred reading material on BPD.