Douching increases the risk of pelvic infections. No pantyhose or tight pants, including Spandex exercise clothes. Washing with gentle unscented soaps and using Ivory Snow on the clothing that touches that vagina. Using an anti-bacterial soap on the groin area but keeping it away from the vaginal area can eliminate the plain old crotch sweat odor even girls can get. Eating as vegetarian a diet as possible and lots of yogurt may help.
Some women react with odor to the latex in condoms or to a lubrication product.
Changing to unlubricated polyurethane condoms might help. Some women react to eating spicy foods or soy sauce with an odor. There are probably a million other foods that cause some women to react. Now, you know your girl, so you can probably think of a way to discuss this with her gently and delicately. But if you need some hints about how to bring this up, write back and let me know.