Yeah, Liz would be a good option to CC first. Her initial wait time for ReinIII is shorter than Katie's so you can get your UPs faster.

Other units you might want to CC from your plat line up would be: Bashira (archer), Lyla (bandit), Odette (mage), Chloe (angel), Fran (vampire hunter), Anelia (pirate), Eliza (witch), and Juno (healer).