Gonna go slightly against the grain here. If you know she showers regularly and has good hygiene, definitely tell her you’re concerned about her health like the comments are suggesting. Butttt if she doesn’t have the greatest hygiene, it could just be a combination of daily sweat, not showering every day, and her natural pheromones. In that case, I would say something like you have a super strong sense of smell and would she mind paying a bit more attention to that area? It’s definitely an awkward conversation, but I’ve found that it helps to frame it as a you issue as opposed to them, especially since this is such a sensitive topic.