It's 'useless' trying to change her mind. = It's 'useless' to try to change her mind.
Drugs are 'useless' in treating the condition.
I made a 'useless' attempt at fixing the leak.
(..) Nothing essential. That's my letter You must have it's interpretation. Dear Monsieur. I learned that my mother has asked you to... To find me. It's useless. I left of my own free will... In order to join my fiance abroad. I don't want to see my mom yet. You may tell her that. (..)1981 To Kill a Cop