
at the lack of knowledge of feminine hygiene.
The vagina is not a body part that you wash with soap or fem washes, or even vinegar every day.
It's a constantly changing environment that should have a healthy balance of bacteria and yeast. If one gets disturbed, the other overgrows and you get bacteria overgrowths (called bacterial vaginosis) or yeast infections. Having an "odor" doesn't mean she isn't clean. (In fact, over washing can cause bad infections and odors) It just means her body is having an internal reaction to something and she needs to find out what's going on. Douches and soaps will only add fuel to the fire. Hydrogen peroxide for BV or vinegar is the best natural options. She should also try probiotics.
ANYTHING can upset the balance of a woman's flora: foods, hormone fluctuating in the menstrual cycle, soaps, tight pants and underwear, health conditions...but if it's happening mostly during sex there could be a protein in your semen that is causing a reaction with her fluids. In some cases your semen could be causing some BV. Wear a condom and have her sit in a hydrogen peroxide bath. Give her vag a break.