From experience with the beta and memory, your wife (and you) will be able to choose which version to play. Either yours with a ton of DLC or hers with none. You should both be able to use the version with all DLC, but not at the same time.
It’s been a while since we tested this though so things might have changed, including my memory…
It’s not a card game, it’s an async autobattler. As long as all the characters are roughly balanced against each other, there’s nothing to be gained other than cosmetics (at the current state of the game).