Trixie remembered the night that it happened. It was one of those nights while she was alone in her apartment when she was feeling so down. Her best friend was gone to chase her dream. Her brother was either too busy with his job or chasing his girlfriend. She got nothing left because the only two families she considered were gone.
They might think that Trixie doesn't have a down moment. That it was impossible for her to be lonely because she has a lot of friends but no. She's got a very happy facade but internally, she is broken.
Blame it on being neglected by their parents at such a young age. To their parents, she and Arthur were a disappointment and they never bother to hide it from them.
Things became worse when Arthur left for the military and then, later on, joined the Twelve Army.
She was alone and lonely.
She might have a lot of friends but there are still those moments when she doesn't feel like being surrounded by them.