I appreciate the struggle you were having with your mom. But I do not think confronting her is the right thing to do.
Emphasizing that your dad needs to step-up would be an important way for you to help your mom. Having an in-depth talk with him is important. Explain that you’re not going to be around, that you’re in college — and eventually will have more of your own life — and not be there to help. If she’s getting worse and making a plan together to help her might be valuable. Working together with your dad and talking with him about your concerns is an important step.
Your dad may offer to go with her to therapy appointment to explain that there are some issues at home. Most therapists would welcome this from a family member.
Secondly you may want to talk to your college counseling center about resources in your area for family and friends of people with mental illness. You may also want to take advantage of the counseling services offered by them. This may help you cope as you continue to grow and take care of your own needs while dealing with with the family dynamics at home.