I could be wrong, but I feel like if May's "skin" was dissolving/coming off, she'd be a little more concerned with getting cleaned off ASAP rather than establishing her friendship with Momo, and then trolling her with the handshake. Keep in mind, May is practically broke at this point; if she needed to buy a replacement outer covering, she may not have the money to do so or would need to spend most of her money on it. May doesn't seem worried about any damage the substance is causing her, so I'd tend to view it more as a harmless prank than "haha, now your hand is melting too".
Of course, I'm probably overthinking this and we'll find out if it's a big deal tomorrow.