I would either ask for more swabs, or seek another opinion or even a referral to a gynae. If it's causing her embarrassment/distress, that's not ok. There may be some more sophisticated sorts of pathology that can be done.

Is she sure it's a vaginal thing? Sometimes people can develop a bit of festiness in skin folds in the groin area (even fungal infections). Check that she's washing these areas well enough too.

I know letting the area out to breathe is the best idea, but in the short term it's worth thinking about using more absorbent panty liners, there are some odour-fighting ones that might help, and she can change them as often as she needs to).

In the meantime, try epsom salts in the bath, about half a cup, and repeat for a few days in a row, see if that helps a bit. If it does, keep doing that a few times a week. I would also get her onto some pro-biotics too.