Thanks for your input ladies. i took her to the doctor and it was in fact BV bacteria Vaginosis. the doctor prescribed ovules for her to insert.
Tell your sister that when she washes down below, she also must wash in between the labia majora and the labia minora, as smegma can build up and cause a not very pleasant odour.
Tell her not to use perfumed soaps. The best way to wash down below is with plain water, use non perfumed soaps and those soaps that have a pH level like our skin. Baby washes should be fine. Tell her not to use any talcs or feminine sprays. Her natural body odour may also be counteracting with any washing detergent, using non-biological washing detergents may be better.
Tell your sister to wash every day like explained above and put on clean underpants every day - and not wear the same pair of pants for more than one day. If she does sweat a lot, she may need to change her underwear more often.
If this does not stop the bad odour, then she should be examined by her doctor to make sure that she does not have any bacterial or fungal problem.
Bicarbonate of Soda, which can be purchased from the supermarket on the bakery section or from the pharmacy is also a good way to eliminate bad odours. But hygiene is of paramount importance.
In her bedroom, get the windows open from time to time to air the room. Sprinkling Bicarbonate of Soda on the carpet before vacuuming will also help to eliminate bad odours.
Good luck.
She could try a cornstarch-based powder sprinkled onto the crotch area of her underpants until she gets cured of the odor.
Gynecologist is the right doctor.