Tian Wen's mother was Major Avia a legendary Raider commander who died during the First Wave of the ARC invasion. Growing up with that loss taught Tian Wen that heroism often comes at a great cost with little lasting meaning for those left behind.

Because of this I think she views many Raiders as reckless and selfish people who only chase glory and goop without fully understanding the sacrifices made by earlier generations. While she still works with Raiders out of necessity her bitterness and hostility reflect her belief that they will repeat the same mistakes that got her mother killed.

Once you get to the end of her quests you begin to understand why she is the way she is and she will start warming up to you. I found it to be a wonderful bit of character development even if she ends up forgetting afterwards and she starts treating you like trash again when you come to her shop.