Before complaining to the management about sexual harassment as you suggested, "Plain Jane" might take a careful look at herself. Is she dressing inappropriately for the workplace (low neckline, exposed midriff, short skirts)? Does she smile too much?Is there candy on her desk, encouraging co-workers to stop and chat? "Jane" might ask a trusted older working woman friend or relative to look over her wardrobe or share other hints.
I would love to get her to elaborate on the "smiling too much" concept. How much smiling is too much? How do you tell? Personally, when I smile at my co-workers, it's a natural smile - I haven't faked a smile since I worked in customer service. So if your natural smiling in reaction to context has you "smiling too much", how do you deliberately not smile without looking like you're being deliberately mean?