This chapter confirmed the Byakugou can counter the acid from a god's dimension. I don't see Mei melting her. Tsunade wins with mid difficulty.
If the starting distance was greater, Mei would beat Tsunade but Tsunade wins low difficulty in this scenario. Sakura dodged most of the acid and only got exposed to a few burns on scattered parts of her body (
You must be registered for see links
).
Mei's acid will inflict burns on every part of her body and once they breathe it in, inside their body as well. Sakura was in pain with just a few scattered burns which weren't strong enough to melt skin (
You must be registered for see links
). Mei's acid mist is strong enough to melt ribcage susanoo and thick concrete walls so her's is more potent or at least more potent than the amount of acid Sakura was exposed to. After all, Mei's acid mist is created by her own chakra, while the acid from Kaguya's dimension is just that, acid which isn't created via ninjutsu, it's just a part of her dimension.
Also if you want to go with this logic, Sakura had to get saved by Kakashi from falling into Kaguya's lava so Mei's lava can take out Sakura/Tsunade. Although by common sense and logic, it is strong enough to melt flesh and inner organs easily, faster than regeneration and with vapourized body parts, there will be nothing left to regenerate. Furthermore, Mei can harden the lava, turning Tsunade into a statue.
