I decided to focus on the sisterhood theme for my Trifles essay, but I am having a difficult time deciding on which points to cover. Would it be...

Sisterhood in Trifles is best shown when Mrs. Peters and Mrs. Hale decide to cover for Minnie. Their mutual understanding of how difficult marriage can be leads them to cover up evidence of murder so that another woman can go free.

The first example of sisterhood is that the women are there at all. While their husbands are there to gather evidence, they're there to help Minnie, who is in jail. They're picking up things...

Sisterhood in Trifles is best shown when Mrs. Peters and Mrs. Hale decide to cover for Minnie. Their mutual understanding of how difficult marriage can be leads them to cover up evidence of murder so that another woman can go free.

The first example of sisterhood is that the women are there at all. While their husbands are there to gather evidence, they're there to help Minnie, who is in jail. They're picking up things she needs, rather than condemning her or ignoring her. Later in the play, Mrs. Hale laments that she didn't visit Minnie sooner; she stayed away because the Wright household was an unhappy place. 

The women are sympathetic toward Minnie, even though she clearly murdered her husband. Their difficulties with their own spouses -- who overlook them and their concerns -- help them decide to cover up Minnie's crimes. Mrs. Peters tries to hide the box with the dead canary, and when she's unable to, Mrs. Hale does it instead. Though they know it's strong evidence, they choose to be loyal to the sisterhood and conceal it. 

The sisterhood between the women and the mutual understanding they have with each other helps them notice the trifles that the men overlook. For example, they notice the erratic stitching on part of the quilt that doesn't fit with the neat and careful stitching on another part. Rather than point it out to their husbands, Mrs. Hale pulls out the bad stitches and fixes them herself.

Ultimately, sisterhood in Trifles is shown when Mrs. Hale and Mrs. Peters decide to gather things for Minnie, when they notice evidence the men miss, and when they decide to conceal the evidence, so that Minnie might go free despite killing her husband.