“She's more consistent than me”
Dictionaries give consistent as "unchanging," but here it means steadily keeping something up without gaps. Tina admits that compared with her friend, who never misses a planned workout, she is weaker at sticking with it. It does not mean the friend goes every day or never takes rest days.
“She never skips a workout.”
Skip means to miss or leave out something on purpose. Here it means leaving out a planned workout. It is also used in phrases like skip class.
“I'm catching up.” / “thirteen push-ups is your goal”
Catch up means to reach the same level as someone ahead, a push-up is an exercise where you push your body up from the floor with your arms, and a goal is a target. The friend can do twelve and Tina can do ten, so Tina is aiming for thirteen. Frank is confirming a concrete goal; he does not claim that eating better will soon make her stronger than her friend.
“I was very specific.”
Specific means clear and precisely limited. I was very specific. means "I stated my condition clearly." When Frank asks whether she will keep training after she wins, Tina points back to until I beat her in line 7, insisting that she always meant to train only until then.