@paragonxxx: There's a gameplan the team can use as a path to victory. Hawkshade seems to be fairly familiar with his mother, he discovered her Cave in Gothic and we can assume he knows something about her skill-set and powers. Both Grimmwald and Hawkshade are former Strigidae so they would be familiar with any of the Arcani arts in Ivana's repertoire. So they may be able to coordinate their efforts with the group to minimize Ivana's strengths and use their advantage in numbers. Everyone in the team is a skilled fighter, though Tessa is probably the weak link as far as martial skill is concerned. Ivana would eliminate her very quickly. But there is a path to victory for the team.
That being said, Ivana would win, LOL. She's a better fighter than all of them. Far more experienced, has much better gear, and will go to lengths that no one (save for maybe Tessa, but she's not skilled enough to implement a plan of action against Ivana) in the team is willing to. I don't know how comfortable Hawkshade would be with fighting his mother, though I'm not sure Ivana would be comfortable fighting her son either, she might though, she's maybe not emotionally conscious enough to care about it too much. She has amazing feats against some of CV's deadliest fighters, and routinely engaged opponents who were more powerful than she was. So I'd pick Ivana. She's too skilled, too fierce, and her gear is too good. Also, no one in the team except for maybe Grimmwald will be able to contend with her on a physical level. Ivana is very strong. She can bend steel bars and uproot trees. She's also very explosive. It comes at the cost of stamina sure, but she's too skilled and her gear is too good.
I'd pick her for a fairly easy win. Though I think the one interesting opponent for her here is Ashley. Ashley can regenerate, is a skilled fighter (though not close to Ivana's level), has decent gear, and she won't get tired. The only issue is that she isn't skilled enough to contend with Ivana, nor does she have the killer instinct you may need against Ivana. With prep, the team would stand a better chance, especially with Ashley's medical resources e.g. chemicals, toxins etc.