My daughter just got back from a summer internship with a nonprofit in a Mexican border city that’s known for violence. She had no problems, and the organization has been working there for many years with no safety problems for volunteers or staff, even when the violence there was at its height a few years ago. While there’s no guarantees, avoiding risky behaviors like wandering around alone or at night, or visiting the types of areas where foreigners are targeted (bars, etc) reduces the risk a lot. If it were me, I’d ask some questions of the clinics about the specific areas and just go in well informed about what precautions to take.