1) MEi has a hidden swordman on her team so she'll very knowledgeable on them
2) She's the leader of the village the consistently produced hidden swordsmen, so she's very knowledgeable on them.
3) Zabuza is very known in mist village, for trying to kill yugito, killing those genin, etc and known there and other places for his 'silent killing' methods, so she's very knowledgeable on him
4) Hidden mist is in her arsenal, so I'll assume with 99% certainty that she can fight through it. why would she have a jutsu that just hinders her?
5) She has boil release which is an enhanced hidden mist, leading me to believe even more that she can fight in mist
6) She's the kage of the hidden mist village, which is often covered in mist, so i'll assume even more that she knows how to fight through mist.
7) Mei Became Kage after Zabuza died I believe(not too sure on this), so he may have quite limited knowledge on her.
Off those 7 points, I'll comfortably state that mei has quite good knowledge on zabuza's skills, along with being able to at least defend herself during his deadlist technique "Hidden Mist: Silent killing technique". Ontop of this, her suiton completely dwarfs that of zabuza's, along with her other deadly jutsu. Therefore, I will go with Mei 10/10.
Mei wins Low diff imo.