kbin can interact with mastodon freely, so if that's something you want to be able to do easily, you might want to switch over from lemmy.
I was thinking you can probably open the user's profile on lemmy and reply to the post from there, but testing that didn't seem to work. I assume that's just federation taking a while though, so I'd say try it anyway. Searching for @name@usersmastodoninstance I mean. I don't see why it wouldn't work.