With her costume Vivica is great. She provides some great flexibility, & that strong defense down from a yellow hero is unique as well.
That said, if you’re lucky enough to have Mother North you have a hero with one of the most coveted skills in the game with that ability to revive. And while her heal isn’t as strong as Vivicas, it also produces minions as shields to help supplement it.
I don’t think it’s quite as cut & dry as the previous responders, & I don’t think you can really go wrong either way. That said my personal experience is limited here. I’m fortunate to have costume Vivica, but she’s still at 3.70, and I’ve never been lucky enough to pull Mother North
Maybe consider the rest of your roster and decide if you’re lacking in either color, or if a healer in one color allows for better combinations elsewhere. Either way, good luck. It’s a good problem to have