Talking to your T about this whole RS esp whether it is not damaging to you sounds like a great idea.
Honestly, if I were in your place, watching s.o. I cared about deeply destroying herself I would need to set pretty strict boundaries to protect myself: on contact/things discussed... Potentially removing myself from that RS.
Sure, how she lives her life it's her decision but so it's mine and I would not play the role of fussing over her, contacting her T, bearing witness to her killing herself... In it.

ETA: Yeah and as I can see Growly just said it and said it better