Minnie Wright is the woman accused of murder in the play. She is never seen but she is discussed and described by the other characters as they investigate the house. Apparently, she used to be extroverted and very outgoing, but after her marriage, she became quiet and isolated from others and from the community. Even though her marriage was unhappy, she tried to stay positive through housework, quilting, and the purchase of a canary, which reminded her of her old life.
MRS. HALE: [Examining the skirt.] Wright was close. I think maybe that's why she kept so much to herself. She didn't even belong to the Ladies Aid. I suppose she felt she couldn't do her part, and then you don't enjoy things when you feel shabby. She used to wear pretty clothes and be lively, when she was Minnie Foster, one of the town girls singing in the choir. But that -- oh, that was thirty years ago.
(Glaspell, Trifles, etext.virginia.edu)
The implication is that it was Mr. Wright's harsh attitudes and refusal to allow Minnie an emotional outlet that led to the murder. Minnie became more and more closed off, knowing that she was unhappy, but unable socially and personally to address her issues with her husband. Societally, she would not be seen in a positive light if she wanted a divorce, and spousal abuse was more commonly covered up at the time. Minnie was an essentially good person, but driven by circumstance to extreme action.