The issue here is mainly that two laws conflict: one, a complete abortion ban at the state level. Two, a federal law, EMTALA, that requires Emergency Departments assess and stabilize any patient that comes in. EMTALA has a few other requirements, like not asking about payment until after treatment and preventing unnecessary discharges or transfers. This is the law that makes it so that uninsured people go to the ED/ER when they are sick, since regular docs can deny you for not being able to pay.
The key part of EMTALA here is that assessing and stabilizing a patient. If someone comes in during a crisis and the only way to stabilize them is to terminate the pregnancy, that is at odds with Idaho’s abortion ban. Basically, SCOTUS now has to say whether saving the mother is important enough to warrant terminating the pregnancy.