I must admit, as a teacher, you seem to have got things slightly the wrong way round. Really, before developing your supporting paragraphs, you need to have identified a clear thesis that you can then use to structure your middle paragraphs. Your main body of the essay should be carefully crafted to support and argue your thesis statement. If you have developed your middle paragraphs first, my strong suggestion to you is to go back over them and to work out what precisely it is you are arguing and trying to show about the differences between Mrs. Hale and Mrs. Peters and form some kind of thesis statement based on that. Does this make sense? You might, just as an example, like to think about this as a starter to help you develop your own thesis statement:
In Trifles by Susan Glaspell, Mrs. Hale is a strong woman who is willing to defy patriarchal authority whereas Mrs. Peters is a much more timid and oppressed figure.
Formulating the key differences in a statement like this should give you a strong thesis statement that will hopefully be supported by your middle paragraphs. A word of caution though: because of the way you have done things you need to be particularly careful that your thesis statement is actually supported by your middle paragraphs.