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.
(..) I wanna go with you. I told you, didn't I? You're not coming home with me. I live alone! My swamp! Me! Nobody else! Especially useless, pathetic, annoying, talking donkeys! - But I thought-- - Yeah. You know what? You thought wrong! Shrek. (..)2001 Shrek