The Question and Answer section for Trifles is a great resource to ask questions, find answers, and discuss the novel.
Sorry, I don't know enough about the stage set to give you a good answer. The state of the kitchen and the bird cage do give clues that the women see and the men fail to see.
“Trifles” are defined as things which have no value and are considered to be insignificant. Ironically, the men who are so determined to find convicting evidence look past the observations of their wives because they're seen as insignificant...
This is a moral judgment call. Covering up the evidence certainly is against the law but you must decide if Minniw was abused and if the end justifies the means.