Like the above poster said, Iruka is good, especially if you have his Y+1 second passive (Teaching Instructions). With that and Gaara you can really stack a lot of shields.

Another option is Summer Ino if you have her - she can be both secondary offense and a little bit of healing too. Plus Fire main's Red Lotus passive will buff her alongside Kushina.

If you want a full on healer you can try Summer Sakura, or Cape/Cloak Sakura if you don't have her. But Summer Sakura is nice because she dodges so she's harder to shut down. I wouldn't put her pos 2 though, probably pos 3 behind Kushina and move Fire main to pos 2 link.

Killer Bee Seven Swords is another one, he'll shield Kushina, Gaara, and himself, let Kushina attack twice (nice, more healing on) and be immune to interruption.

I dunno which ninjas you have out of these but hopefully one of these can work for you.

Thank you.