(An unlisted trait of her sub skill conditional, like most similar ones, is that she does not affect Robot-type cards) (Another reported but unconfirmed detail is that only one Chelsea works per card)
Her subskill is only a +damage boost, not a skill power boost (which has a more proficient effect), and most of the better attacking cards in the game are girls, except that thanks to matching icons (and the otherwise unconditional nature of the bonus), she makes a very strong sub card for Noveau Rich Penguin- and he is one of the best cards in the game, full stop! Penguin aside, she can also be used to decent effect on General Gorilla, who is also no slouch in the powerhouse department. She also fits well with Loki and Thor. That's not a bad set, though Penguin steals the show.