But when she went to Iraq as an Army specialist, she found herself having to shoot and kill the enemy.
"When you take another human being's life, it's like maybe part of you, like your soul, you know? You just leave it behind. It changes you forever," Morgan said.
Women aren't supposed to be serving in combat positions - it's against U.S. policy, CBS News correspondent Kelly Wallace reports.
A new documentary to air on PBS called "Lioness," describes how women in support roles are finding themselves in ground warfare.
"I guess it's hard to say that, yeah, we've been in combat 'cause I was just doing my job. I mean, we all joined the Army," Staff Sgt. Ranie Ruthig said. "We didn't join the Girl Scouts."
"Lioness" started as an ad-hoc policy. Women, like Spc. Rebecca Nava, joined all-male combat units to search Iraqi women and children.
"And they were just so surprised to see females and how different we looked from them," Nava said. "And they would be like, 'Ooh, so pretty.'"
But benign search missions often turned into street warfare - a situation the women weren't trained for.
Weren't they scared?
"Nost definitely," Nava said. "We all had families that we worry about, will we see them the next day? You know, was that a last goodbye or was it a final goodbye?"
Battle buddies Morgan and Ruthig went on missions together. One day Morgan found herself all alone and the target of enemy fire.
It's the longest few seconds before you pull the trigger. Seems like it's all in slow-mo. But you just got to keep tellin' yourself, it's either you or them.
"How does everything you've seen and experienced, how did that change you?" Wallace asked.
"I think I left a piece of, piece of myself," Morgan said. "Maybe the innocence, so to speak. Maybe I left some of that back over there."
The Pentagon made Lioness an official program in January and now trains women to operate combat weapons, but still bans women from direct combat roles.
"They need to be able to use women in this way and they will probably need to in future conflicts," said Meg McLagan, one of the filmmakers who made "Lioness."
"I thought at the time, you know, the only way to end this is to just take my own life," Shannon said.
She has since found strength staying in touch with her band of sisters.
Today, they're missing someone - their company commander, Maj. Kate Guttorsmen. CBS News arranged a surprise message from her.
In it, she holds her newborn baby in her arms, to show to the sisters in her heart.
As Shannon said: "I mean, we're like sisters. We're like - we're closer than family because, my god, we've been through combat together."