"The unknown is always the scariest part," she told ET. "Is the chemo going to work? Is the radiation going to work? You know, am I going to have to go through this again, or am I going to get secondary cancer? Everything else is manageable. Pain is manageable, you know, living without a breast is manageable. It's the worry of your future and how your future is going to affect the people that you love."

Doherty praised the supportive surgeon who performed her mastectomy, but said that the aftermath of the procedure still involved a lot of emotional and physical adjustments.

"It was traumatic and horrible," she said of her fitting for a new bra. "I didn't think anything of it at the time, then my mom went with me and I broke down crying in the dressing room and ran out. And then sat in the car crying."

Doherty has undergone three out of eight rounds of chemotherapy thus far, and candidly described her intense post-chemo experiences, citing her husband as a constant source of support.

"After my first treatment I lost 10 pounds, instantly. You're throwing up and the last thing you want to do is be in a car," she said. "You don't want to be moved, you can't eat. But my husband has to, you know, pick me up. He puts me in the car, he buckles me in, and he drives me to my oncologist and they hook me up to an IV and I get hydrated. There's nothing going in my body, it's all going out."