She's a relic exclusive, so only from her character-specific relic (which is available on Wednesdays). I would suggest buying a 10-pack (if you have enough Theonite) because the bonus relic gives you double the chance of getting a gold.Thank you! But which relic would be the best to get her skin out of? (Hopefully I'm making some sense.)
This page has more info about drop rates: http://forum.skullgirlsmobile.com/threads/official-fighter-relic-loot-rates.213/
Good luck if you decide to try to get her!