Gotta love it when the karma bus runs them over, backs up, and does it repeatedly.  IMHO the guidance to SS has to be to protect himself from them and their bullshit.  He is a young man who should be focusing on himself and his future.  Sadly his BM and sister are write offs.

He needs to write them off.

My SS had some of this drama in his SpermClan life.  Guilt from his SpermGrandHag who guilted him incessently and tried to manipulate him into helping support his three younger also out of wedlock Spermidiot spawned half sibs by two other baby mamas.  We defended him from all of that. 

He is thriving in his life.  The whole SpermClan is continuing their multigenerational crash and burn.  His three sibs include spawn #2 who is on the dole, #3 who is serving a long prison sentence, and #4 who is not far behind the inmate.

Find a psycho terrorist/therapist who will keep a theraputic foot up her butt rather than facilitating her manipulative crap. Get the web cams and audio recorders up so she can't back out later.  Make sure the intake desk and everyone else sees and hears her self harm blather and threats.  My guess is she is full of shit and this is all pure manipulation. 

However, I would make her life a living hell and do everythign possible to prevent her from taking her own life until she reaches the age of majority. Even then, not in my house. 

Lock up every med and chemical in  your home, screw shut all of the windows, take down all of the closet rods replacing them with spring loaded shower rods, lock up all belts and shoes with shoe laces, take down all of the ceiling fans, confiscate her shoe laces when she arrives, etc.  Get a hand held metal detector wand and scan her when she arrives, when she leaves and periodically through the day and night when she is in your home.  Do the same with a thermal imaging camera. That will show that she has somethign stashed on her body in her her clothing so you can take further action.  They are available for purchase on line as attachments to smart phones for a couple hundred $.

If she goes through with it, make the odds far more likely that she will do it at BM's rather than at your home.  All while engaging the authorities and every mental health option at your disposal.  Getting the kid help is key. But protectiong you, your own mental health, DH and his mental health, and your home from her taking her own life when she is with you has to be a huge priority IMHO.

When someone tells you that they are going to kill themselves, thinking about it, feeling like it, believe them. Then hog tie them (figuratively of course), get them the full meal deal of all help, assessments, and interventions available.

When she blathers later that you did not care and did not help her, show her the spreadsheet and receipts for what you did do and what you spent to keep her from killing her self on your watch.  Every appointment, ever ER visit, every camera, lock, etc... that you bought and used to keep her safe from herself.  Keep a journall and record every LEO visit that you engaged calling 911 on her behalf, etc..

Question. Does the leave an infant at a fire station rule apply to toxic preteen and teen spawn?

If not, too bad.

With the recent conviction for manslaughter of the parents of a minor school shooter, I would not put it past prosecutors going after parents/sparents for the same charges in the case of a teen committing suicide.

I am in the "not on my watch kid" camp.

You typically cannot diagnose anyone under 18 with personality disorders, as they have not fully developed and matured yet. It doesn't mean she doesn't have one, but they won't diagnose that young. 

Personally, I think this is full blown manipulation and SD is trying to see how far she can test limits and push people to get what she wants. If SD actually was suicidal, her suicidal ideation would demonstrate plans that are likely to be successful - i.e. not jumping off the roof of a house. I think SD gets whatever she wants at Crazy 's house and there are no rules or expectations, so whenever OP and DH or school or friends or anyone else places expectations on SD, she claims suicidal to try to manipulate those expectations; to make it seem like she can't handle them. 

She likes chaos. It keeps life interesting. Maybe one day she will be diagnosed with BPD or something similar. 

Nope, no one should come running. They should call 911 to get LEOs there ASAP to address the manipulations with hand cuffs and a 24+ hour pshych hold while everyone else enjoys SS's exciting campus visit.

Time to call her bluff with escalating official consequences and envolvement.\

Not a particularly empathetic or solid psych care perspective I know. But... it has to happen IMHO.

Play stupid and crazy games, win stupid prizes appropriate to the fake issues you are leveraging.

Hopefully fake anyway.  Heaven forbid she actually hurts herself or worse.

Not on my time kid. Do that shit after you are 18.  It wills till break my heart. But it will not be on me.

If I were her parents/sparents/brother.

Perhaps you should remind DH that this upcoming weekend is about SS, if he (DH) thinks he will need to go running off to help poor little SD, it's best he stay home to keep her little world happy. Then you and SS go. Make it fun, chat up the other parents at the event while he gets to do the activities and meet what may be his fellow students. He can call Daddy and fill him in after the events. 

Unless DH makes it clear to SD that while he does love her, he will be out of range to come running should she have another dramatic episode. 

But, this is certainly a good consequence

Time to end life as she knows it.  A good baby sitter is not one who is that manipulative or potentially suicidal. If I were the family, that batshit crazy manipulative spawn would not even set foot on my lawn much less in my home and for F sake she would never be alone with my infant.

Stop mitigating for this kid and start keeping every available foot up her idiot ass. This is not insignificant innocent crap. This is top tier stuff that needs top tier support and top tier consequences applied without any attempt to minimize those consequeces whether she is lying her ass off or not.

In my mental health care laymans opinion of course.