She sounds really strong, but keep in mind the strength of her heal is rebalancing the health of all of her allies before a 15% heal.
The best strategy for beating a team with her in it is to leave her for last. I use a very debuff heavy team (Zader lead, Boba, Barriss, EP, Sid), which makes it sound like the other side's Barriss should have a field day against my team.
Barriss' heal is virtually useless if she has no allies. Take out her allies first and save her for last. Don't worry if she heals once or twice, you can still take out her allies with a decent team.