[the-dream]

Your girlfriend doesn't need to get tested, she just needs to get treated. If your infection cleared after medication then came back when you fucked her again then she has it. How gullible/unaware is your girlfriend and how likely is she to fall for a toilet seat story? If you were to take her to your doctor to be treated, would she likely ask questions like "can I really get it from a toilet seat?" or would she just be silent and shy and get out there asap?