Shannon Dominguez, 43, and her boyfriend called 911 after observing a small boy left alone in a hot vehicle outside a store in Longmont, Colo., Fox affiliate KDVR-TV reported.
When police arrived, however, it was Dominguez who needed an ambulance.
The child's mother, identified as 27-year-old Kristina Riddell, reportedly became enraged when she heard the couple on the phone with police.
Riddell allegedly punched Dominguez's boyfriend, Alan Mason, before running the couple over with her white Honda.
"All four windows were rolled up. And it was in the direct sun. It scares the heck out of me. It’s some innocent child might die," Dominguez told the station.
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