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.
(..) under siege, no family to guide her or protect her. Her last relation thousands of miles away, useless, dying. Don't say that, Maester Aemon. A Targaryen alone in the world is a terrible thing. (..)2015 TvShow: Game of Thrones Title: Kill the Boy Season: 5 Episode 5