"My daughter called this morning and told me she had discoverd a tampon that had been left in for 3 weeks! She said she had not been feeling well for the past couple of weeks, but nothing major. There was of course some odor upon removal. I've never known anyone who has experienced this, so just wondered what if anything she should do?"
She needs to have removed ASAP as this can cause a deadly staphylococcus infection call toxic shock.
If she wants to, she can take three full caps of oregano oil three times a day. This helped me with a mild staph infection.