How strong was kushina

[Meowazziel]

high jounin lvl i think.
or low kage.

Being a jinc, holding down kurama (with chains), able to take down some genin or chunin kid, while she wasnt graduated yet.
That kinda suggests talent.

Her ninjutsu style is said to be similar to naruto.

but in the end we lack info.

 

[Shadow Abyss]

We didn't see much of her, but based on the few feats she has shown so far I would say she is mid to strong Kage level.
She is able to restrain the strongest Bijuu and is even suggested she could take it down with her, all of that while half dead. Without her help Minato wouldn't be able to suceed in sealing it in Naruto and even the so hyped Hiruzen admits he can't hope to pass through the barrier she raised.
Her techniques are overpowered.

 

[Nazgul]

Stronger than Mei U_U after all she was able to hold down the kyuubi while in a weakened state.

 

[ShockwavvE]

She was stronger than Naruto