Sarada knew nothing about her eye or that she even had it activated , which probably has something to do with her development , but after she finds out about it she has perfect control over using it and turning it off, she doesn't even use handseals to activate it unlike the others , except in the movie, and hers seems to be directly tied to her emotions
I think Sarada is still at 1 because of the powerscaling between her and her teammates, she isn't easily intimidated , because her emotions don't build up to trigger anything , like Sakura she will probably release them all over you house .
Obito unlocked his because he was scared and thought he was going to die, Sarada and sasuke seems to not be as bothered by enemies trying to kill them
Sasuke held a sword up to Sarada and she didn't flinch , she just caught an attitude , so obito that would've been and mangekyo sharringan moment
If anything Sarada unlocked her's through determination and willpower alone with out even noticing