Read her passive and her scaling. You'll find your answer.

That's where you are wrong, my friend.

Her passive enhances critical hit rate, ergo her injury. I don't really know why it is spelled this way here, but i have checked with a few people in CN servers and for them it's the critical damage that is increased with each hit. Basically, the more you hit her, the harder she hit you back.

Unfortunately, too many people spread misinformation unknowingly and this usually cause even more damage, since in the end one can't understand what is the truth and what is just a guess.

Back to the OT: Kushina's scaling is the reason why she is considered a "bad" character in CN. Since she increase her crit dmg, this stat becomes negligible once you aren't critting enough times. But there are far better characters at higher power that works much better than her. So she is in this limbo where she need high power to work properly but at high power she is lacking utility-wise compared to more advanced ninjas.

Jib Edit: Regardless of if misinformation is given or not, I am sure most of the community is not giving misinformation with ill intent. Most are just here trying to help and I think that being kind to one another and sharing knowledge is better than being negative and mean.