It may be a benign lesion called a seborrheic keratosis (SK). Dermatologists can often diagnose these clinically with a naked eye or dermatoscope (without biopsy). Unfortunately, I can't say it's a seborrheic keratosis based on the picture. Your partner should have the lesion checked again to make sure it's not a melanoma.
Moles don't usually grow that fast. It's probably something inflammatory - granuloma faciale, sarcoidosis, fixed drug eruption - something like that. The only way to know for sure is to biopsy it, which is an easy office-based procedure. Also, it is important to rule out melanoma. I recommend going back to your dermatologist for biopsy.
