So long as you change your pad or tampon regularly and shower daily, there is no reason that anyone would smell your period. Menstrual fluid can begin to smell after a few hours, or sooner if it’s a heavy flow day but this is rarely obvious to other people - have you ever smelt anyone else’s period? If someone has an obvious smell (especially if it’s fishy), they should see their GP - Its awful that people are mean to her. If you are friends with her, perhaps have a quiet chat with her and tell her that her problem might actually be easy to fix. Alternatively, let your year adviser know that she is being bullied.