Her mother who is an alcoholic
If it were me I would start with Al Anon, the 12 step group which is an offshoot of AA for family members of alcoholics, etc. In addition to what the others recommend.
That would be a good way to start. If she has her own substance abuse issues, she will find her way to another group as well, g-d willing.
A 12 step group is not mental health counseling. It is support, community, a way to understand life, etc.
If she lives where there is a university medical school they have psychiatric clinics with sliding scale services.
A county hospital should have a psychiatric clinic which might have sliding scale services.
If she is in college there is a counseling center that will be free.
If she has drug or alcohol issues County Mental Health will have a Substance Abuse department.
If she is not working or low income she can apply for medicaid. Actually, she should do this.