So far, you may have a very broad topic. The way to narrow it down and find something researchable is to see what the conversation is around your topic.
Here is a broad topic idea: female friendship in City of Ladies by Christine de Pizan
This is not a thesis statement - I can't write that until I do research.
What do I need to know in addressing my topic? This is a creative process and relies on your curiosity.
Search in the below resources and pull together any narrower topics and keywords you might want to investigate.