Mei has way better on-panel showings, portrayal, knows how to fight inside the Hidden Mist (she is a user of the technique as well), and has an anti-CQC bloodline limit: Vapor Style. Sooner rather than later, she will overwhelm him with the scale of her ninja arts.
Mei wins more times then not as Zabuza is outclassed in a Mid-Long range game as Yoton could pressure him while her Suitons beat his own as well as ragdolls him. If Zabuza tries to get close to cut her down then he runs into the risk of Futton melting him. It's just a matter of time before he dies
Zabuza is jonin level,mei is kage level.
Zabuza died to Kakashi in OG naruto,
Mei is Fighting against madara,and melted sasuke susanoo which is more defensive than gaaras sand.
I dont see why Mei just melts zabuza face off.