OCEANSIDE, Calif. — Among the scores of memories that Tiffany Lucas collected during her years as a Marine gunnery sergeant, she wears most of them with pride.

When a superior ordered male Marines not to curse in front of female Marines — as if the women were too delicate to take it — she spit an expletive his way. When other women selected the skinniest male Marines to carry on their shoulders during training, as if from the battlefield, she instead picked the heavy ones.

But the memory that has haunted her was her failure to push back against a commander who told her not to report a young female recruit who said she was raped by a male Marine, who, Ms. Lucas said, went on to assault two more women.

“I was too weak to stand up to my commanding officer,” said Ms. Lucas, who served in the Marines for 11 years, including in Falluja, Iraq, in 2006 and 2007. “I really wish I had done something. If I could go back in time, I would stand up for her.”