I don't see any issues with the 'love' theme and it isn't cliche at all with the premise of the movie

She's thrown into the world of man kind during one of the worse wars in history and is only ever shown how horrible people can be and how bad the world is and at some point even gave up fighting for them because of it.

When she sees Steve and his men continue to risk their lives after she says she is done fighting, and Steve shows her the love and compassion that exists in the world, it's a reason for her (someone with near no knowledge about humans) to continue fighting despite the world having wickedness in it which is exactly how the real world works, love and compassion triumphs over evil.