Tell her that everything you've worn and everythign near it and anything you've even touched for the past 3 days needs washed. Find the shampoos that are designed to fight lice, though there is a potential that the lice may become resistant, in that case use somethign such as full fat mayonnaise, olive oil, Dippity-Do brand styling gel, or Hair Clear 1-2-3, which will suffocate the lice, and becasue they do not count as cemicals, lice cannot become resistant. Also, lice eggs, called nits, are ot be removed as often as possible, a specialised lice comb should come with proper shampoo. Use a regular comb or brush and hair clips to remove tangles and separate your hair into sections. Then use your lice comb and go through each section of hair from the scalp to the end of the hair, removing all of the lice and their nits. After finishing each section, search again for any lice that you may have missed and remove them. Your parents are encouraged to assist.
This is coming form a person that has never had lice, though grandma likes telling me horror stories.