Ancestor believed to be from Ireland

According to research by my paternal aunt and records I have found to date, I have a 3rd great grandmother who was from Ireland but we have no idea where in Ireland she might be from as we cannot find where she is from or when she immigrated (but marriage record says 1858 she was in Waterloo Region of Ontario Canada, her father is Will Shields and I believe her mother's name is Catharine (it was a contracted form on the paperwork if I have the correct marriage record).