I think the idea is that while any person could probably connect the dots, in a courtroom the fact that they were around the clinic is purely circumstantial and therefore insufficient to prove someone got an abortion.
It cannot, and they don't care that it cannot. The cruelty is the point.
Abortion is legal up to 12 weeks in Mexico. As a result, anyone showing up even at peak 12 weeks would not be visibly pregnant from outside the car.