In the last 20 years I've had three friends whose sons have committed suicide, all violently - one shot himself, one drowned himself and one hung himself.
Absolutely devastated the families, as they were all found by family members. They ranged from 17 to late 20's in age and only one left a note - which didn't really make sense.
For one there were some warning signs but so subtle they they didn't realise till after the event.
The families never recovered from it and all blame themselves in some form for not seeing it coming, if only they had come to the same realisation as your sister.
Anybody out there contemplating suicide - there is a future and help available no matter how bad it seems.