Forgot to add (because my post wasn't long enough) - we defintiely experienced the throwing, as well as slamming doors (her bedroom door doesn't close properly even now because it's been slammed so hard so many times). She also threatened self harm on occasion. We did take it seriously - at one point, when she was a teen, we had suicide hotline numbers prominently available in her room. However, I honestly don't think she was suicidal though, as much as overwhelmed and just not knowing how to deal with it. We went through four or five therapists before finding one we had for five solid years (not always weekly, but always at least every month or two) who provided a great outlet for her and often for us as well in family sessions.
She hasn't seen one for a while, but is looking for one now as she deals with her next big life transitions. I'm not trying to overshare or make this about my own experiences, but I just wanted to let you know that you're not alone. It's hard to describe but although I think you obviously should never ignore threats or violence, I also think you have to take into account the source and when such threats are uttered. If my dd19 ever said she felt depressed, let alone suicidal, I'd take immediate action. However, with my oldest, I think at times her saying "out there" statements ("I hate you!" "I can't take it any more") was a way of getting out her feelings. I hope this isn't misinterpreted; we did take her seriously and did not ignore her, ever, but at the same time, we knew sometimes things came out more as a reflection of emotions than any actual real intent or feeling (if that makes sense).