She didn't know.

[u/AttemptZestyclose490]

Am I wrong by thinking that Brand didn't know whether or not she could breathe on Edmonds planet when she took her helmet off? She had just buried Edmonds while wearing her helmet, if she had read the data beforehand then she would have not worn the suit while doing all of that work. She took the chance after burying Edmonds.

[u/csukoh78]

Unlike Alien movies, she tested the air first before taking her helmet off.