WOW, that is quite a shock and I am sorry, but it is good to find this out because now help can be given.

I have no advice from the standpoint of parenting (I never had kids) and I never had such a serious problem as cutting either, but I KNOW depression, and only professional councelling/medication/therapy etc. will help. It is an area you cannot control with simple determination.`

You will need to find a way to confront her (and I would think that you know her best and can find a way)....but don't delay. the next episode could be the worst.

Prayers to you and she.