Earlier quoted context omitted.
The word has lots of original meanings, many of which are quite disparate: "Large price increases could trigger demands for even larger wage increases." "His unpleasant remark triggered an argument that almost cost them their friendship" "Studies show that lack of water is the number one trigger of daytime fatigue for Americans." And so on. The usage you're citing is relatively recent jargon.
Yes, that's exactly the problem: it's psychological jargon. People started using it in a jargon way to try to explain to others what PTSD is like. It was supposed to evoke compassion from people if they understood what triggering someone was. Instead it became a point of ridicule and mockery, "oh, I hurt your feelings ? Did I trigger you, sweetheart?"
The word, when used as a verb, originally refers to a consequential relationship between two entities. According to Webster's something triggers when it "initiates, actuates or sets off" another thing. It appears her usage of the word is entirely and completely correct.