The full-face respirator Amelia dons to enter the CO2-filled kitchen would ensure her death. It is the type that filters particulate contamination, and very low levels of fumes. It does not provide breathable air to the wearer, as would a SCBA-type face mask like fire fighters wear. She should have an air tank strapped on, with a hose running to the mask. If the room is full of CO2, there is no air for her to breathe, and she would pass out almost immediately.
Other than to prevent cross-contamination of the crime scene, (which they have blatantly disregarded thus far in the show) there was no reason for Amelia to don the coverall suit to enter the CO2-filled kitchen. CO2 would not have detrimentally affected her skin or clothes.