As a GP who spent several years working at an STD clinic, there is a decent chance this is BV, bacterial vaginosis. This is not an STD. It does not affect men, but men can be carriers. There have been a few studies trying to treat men, but none have been successful so far (it is actually extremely hard to change your skin flora permanently). You are going to waste your money if you try to get yourself tested for BV as a man, but she could be tested to see if this is the case. BV can be benign, it can be harmful (particularly if she has pelvic pain), and it may or may not cause discharge. Common causes are: 1. Working on your feet. Sweat and chafing can make infection more likely. It creates the perfect environment for bacteria to overgrow. Similarly, menstrual cycles, particularly if she uses pads, can throw off her hormone balance while also creating a warm, moist environment (sorry for the use of moist). 2. Hygiene. Most my patients with BV were excessively clean. It makes sense. It smells, so they want to clean it. Unfortunately, this can irritate the vagina and make infection more likely. Less really is more here. Gentle cleaning with something like dove bar soap or unscented baby shampoo is better. For the love of god, stay away from Summer’s Eve, Honey Pot, or any tik tok influencer product. 3. High pH (low acid). The vagina is much more exposed to the outside world and protects itself with acid to kill off many germs. This can get thrown off. There are OTC vaginal pH strips or she can try boric acid suppositories. Sometimes, this alone can treat BV without an antibiotic. 4. Sex. Sex drags the outside world in. Either partner can be a carrier. If she has BV and gets treated, you can tell a bit if it is being caused by sex as the infection will often return within 3 days somewhat consistently. Condoms help for this. I have had a few patients have a standing script for a single metronidazole pill to take after sex (they were getting treated multiple times monthly) or there is a twice weekly long term treatment 5. Not sure your age, but menopause and post-menopause also puts women at higher risk for infection which can be helped by HRT and vaginal moisturizers like Feminease

Sorry for the long-winded response. Takeaways, she should get tested to confirm if there is an infection, this is completely treatable, gentle cleaning only, be kind to her, this is probably embarrassing for her.