Still, Mew isn't some Pokémon nobody's heard of. It's just believed to be extinct, in the same way that most people in the anime think that Aerodactyl and the other fossil Pokémon are extinct. So even if her memory of the 1st movie is still gone, Misty presumably knows what a Mew is. And for all we know, any or all of the group could call Misty up on the telephone occassionally; that's what friends tend to do when they can't meet in person. If that's the case, they'd presumably tell her about things like meeting Legendary Pokémon, and thus Misty would know Mew still exists.
Sure, there's nothing to specifically indicate that, but the explanation is logical enough.
Sure, there's nothing to specifically indicate that, but the explanation is logical enough.