Well - let keep two things apart.
Cutting is not suicide.
Cutting is a way remove heavy stuff from your emotional bagpack. Some use a therapist, some are lucky to have someone they can trust, some works things out by seeking lonelyness and some cut.
All the methods works well, but cutting leaves scars and there is a risk of infection.
If you want her to stop cutting, you should help her to find another way to get her heavy load off.
It doens't take a treatment center.
Who can she talk to? A social worker, a priest etc. Try to be creative. If you know that going to your mother would be equal to having her locked up, help her to find another adult she can talk to. You don't need to involve your mom.
I havn't met a person, who once in a while stumble over events in life, which takes extra effort to work out. It can be people loosing their lives, watching a traffic accident etc. We all need to find our way to deal with such things.
Create an account and p.m. me. Create a email address for this purpose, so you can remain anonymous.