So, a medical ninja can't crush an eye?

[Kakuzu Jr]

Because plot.

 

[TheEvilOne]

In a combat Sakura would show no mercy but in a situation like this I can understand why she is trembling. She is about to kill/blind the man who saved Naruto.

 

[Honord Sage]

She was about to do it and she has to be careful to hit it. She doesn't want to hurt Obito. I don't know why Obito isn't doing it himself. Plus she almost did it but Madara came in and we all know that he is leagues above her in speed.

Obito said He is losing control Black Zetsu thats why. And Medical Ninjas have kill others to protect their patients and She has to do is remove an eye from a dying Man Rin did to Obito.