I'm a Victorianist as well, and my Victorian lit professor during undergrad stressed the importance of learning French, since you typically find it in many texts throughout the period. Since you're interested in women writers, Charlotte Bronte comes to mind as a writer who uses the language a lot. There are a few French parts in Jane Eyre, and Villette contains a very large amount. I'd definitely say French is the top choice, and German would probably be second.