I'm an outpatient therapist in a mental health clinic. A few main thoughts here..if she goes to the ER she will likely get her meds. Will they call child services? Maybe, this may depend on several factors. Perhaps she can have someone watch her child for a few days while she goes to inpatient (should only take about two days) and gets medication. Secondly, if someone is hurting someone else/self/etc. in front of you, you can call 911. Additionally, you should have some sort of Crisis Services hotline in your area to call for mental health emergencies. As for therapy, she should be able to get free therapy if she finds a clinic or psychologist's office that has PhD interns. These places will sometimes offer free therapy if you agree to see an intern. Lastly, this appears to be causing you a significant amount of distress, which I understand...have you thought about some therapy for yourself to help you though it? .
*Info provided is based on the laws in the state I live in..you may want to dig around and check the laws in your state.