Relm's setup is pretty simple actually cause most of her equipment is mage oriented to begin with. She does have some exclusive gear but mostly just pay attention to her MAG stat and if you are worried about her being K.O. then just keep someone with the Cover relic in your party.

For the most part, just keeping her in the back row should work out. She does have one special relic to look out for called the Fake Mustache which changes her Sketch skill into Control, which works like the Tamer class in FFV. Its great for teaching Strago Lores.

There is no protection from Charm I'm afraid, its a special status affliction so it can't be protected against, even by a ribbon. If you have Life 3, you should cast it on whoever is afflicted and then just kill them. For the most part, don't fight the Woman part of Chadernook, just defend or buff your party. You can only win by killing the Demon form.