She's always been portrayed as a low-key, highly capable woman. Her intelligence, blunt personality, yet being able to sport and provide every whim Varrik spouts out just, makes her a character that the surrounding agents no take much notice to her, which is to her benefit.
I loved her fight scene. She has amazing combat skills and damn the way she moved in that suit, it was like she was a bender! I also could not ignore that tongue click and grimace, LOVED IT! Its about time Zhu Li got some screen time.
I have a sense that it's not love that she has for Varrik, but more like pure interest, curiosity and a bit of idealism. There's no doubt the man is a genius, he's just a very larky, clownish, idiot, pest of a genius. She on the other hand keeps cool and slips in and out easily, I would not be surprised if she was some kind of Top Secret White Lotus member.
My thoughts is that she's not doing it for Varrick as much as it to kick Kuvira a peg, by infiltrating the inner circle and manufacturing the weapon for Future Industry for the people to use to fight against Kuvira.