In the play Trifles, what is Susan Glaspell getting at?

Really, you are talking about themes. These are the underlying messages or ideas that Glaspell is trying to convey. Check out the GradeSaver link below,

http://www.gradesaver.com/trifles/study-guide/major-themes/

how sometimes that the things we overlook are more important than we give them credit for being........in this case the evidence and more importantly....the women