Zee told ABC News that after feeling a "lower back spasm" at home that "takes your breath away," she continued to rehearse.
"By Wednesday, I went to see a physical therapist for the show, Gina [Minchella], and she said my pelvis was forward and an inch off," she continued. "I came back the next day, and [my pelvis] was backward and an inch the other way. My pelvis was just moving all over."
"My pelvis is very loose and unstable...because I just had a baby," Zee, 35, added.
Zee and husband, Ben Aaron, welcomed their first child, a son named Adrian, last December.
"I was crying not just from pain but I was more fearful and more frustrated because at this point in the competition every single minute counts," she explained, "especially for a non-dancer repetition is everything. It gives you confidence...and without the ability to do that, it's scary."
Minchella told ABC News that Zee was diagnosed with sacral instability along with a lumbar or lower back sprain.
"It can happen to any person," Minchella said. "It happens a lot to women because our hormones play a huge role in the ligaments in our pelvis."
"For someone who is dancing with extreme conditions from flips to lifts and one-legged turns and all that, this kind of thing can happen a lot faster," she added.
Zee said despite her injury, she plans to take the ballroom floor on Monday night.
"It's not like I'm taking a risk that I'm going to injure my back for the rest of my life," she added of why she's competing. "I'm planning to [perform,] so we're going to do everything we can to rest."
The meteorologist continued that she's planning more physical therapy sessions with Minchella to manage her pain.
"I've been so grateful, especially after the C-section, that my body got back so quickly. I knew I had to get my core strength back and do everything that we were supposed to do. I knew that this was a possibility. It's just unforunate that it came at this time," Zee said.
In the finale, Zee is up against contestants Nyle DiMarco and Paige VanZant. The three will battle it out to see who will take home the coveted Mirror Ball trophy on the two-night season 22 finale of "Dancing With the Stars." It begins Monday at 8 p.m. ET/PT on ABC.