Ash becomes Damage Immune but not CC Immune when she uses her ultimate. Your Evil Mojo will make her be unable to knock back/chip at your team, and if she is low HP be unable to be reliably healed as she returns to the HP she had before Evil Mojo
Ash's main strengths are her high HP and her Knockback abilities. Pips Ult can take that away from you for 4 Seconds. If he Picks up Moral Boost, resilience might be a good choice as you normally have high HP and Damage Immunity with her Ult.