Heyo,

Kushina is really super tanky herself. In modes for example such as arena she's super easy to be nuked from heavy buffed fire element ninjas, for example Itachi Susano'o, because the elemental counter does add a additional percentage of damage which is almost equal to a critical hit. You sadly cannot do that in pvp, because of the element resistance. Shira, as above stated, is a very good option to nuke her down, since he is full Tai and he hurts a lot. Another option is to use Kushina yourself with Edo Itachi and Hokage Minato for example.

Or removing her Immunity to stop her does work in general. Another idea, you can run clones so she won't hit with her standard your main formation ninjas, get rid of the support ninjas of her and then you won