How do I tell a woman I just started dating a month ago that she may have a nasty problem?

I've have a few long term relationships and hope to eventually settle down and recently met a nice woman online. We had several dates meeting in public but a few days ago she asked me to come over to her apartment after we finished our meal to have coffee. Well it turned out to be more than coffee and you know what happened next. Everything was fine and not rushed but at one point as my face was in a certain part of her anatomy. There was an awful smell which is not supposed to be there so I backed off and luckily she did not realize that I pulled back.

I have been with enough woman to realize that something was wrong and it was not a sweaty odor. However I was so startled by this and do not know how to tell her without offending her. My sense is that she needs to see a doctor based on what I read online and it is probably very common what she has, but clearly she was not aware of it.

Has someone on here encountered this before and if so what did you tell her?