Before you have the talk with your mother, do your preparation. What are you going to say? What will she ask? What will you reply? Don't ask a question for which you don't already have an answer.
I suggest that you own the situation and define it. This will give you the opportunity to express it in terms that are favorable to you. This may be a lot harder to do than to say, she is your parent, after all, and some things are easier to say to friends than parents.
If you can, take the lead and put the burden of explanation on her. She found female clothing in your apartment while she was snooping. Then, having found those garments, she left without even discussing it with you. Is she ready to explain why she was snooping and why she refused to talk about it?
Stay focused. Stay on topic. Don't let the discussion wander into other, less favorable areas until you are comfortable with the answers to these questions. ("We can talk about that after I get answers to my questions.")
<sigh> Good luck.
Best wishes
MsVal