Oral Hygene

Nobody has told her because it would be offensive to do so. She may have a health issue that causes the odor that she cannot help. Many people have great oral hygiene, floss, use mouthwash etc. but still have bad breath due to gastro problems or other issues beyond the mouth itself. Chances are she already knows about it and bringing it to her attention would only make her feel more self conscious. Next time you're chatting, just pop a mint in your mouth and politely offer her one as well and leave it at that.

My husband tells me when I have bad breath.
I always try to have a mint or gum around.
I remember when I was a teen my brother use to make fun of me.
I know garlic tablets helped me for a while.
I use to buy them when I lived in CA.
I have not since I moved here. It is usually a stomach or tooth issue. When there is bad tooth it can let off a terrible smell.
As for telling someone, you will offend them no matter what.
O.k. most likely.
But it is in a church setting so maybe they will show Grace towards you after you say something. You may change their life but first you will offend them.(or piss them off)
Good luck!

Carry altoids or breath mints with you and offer her one or a few before practice or after. Since you just joined the choir, I am not sure if you are friends with anyone yet, but maybe you could ask them nonchalantly about this, but not sound gossipy. I am not sure that is a difficult situation. My dad has halitosis because of a medication he takes, but it is much easier to be honest with dad than a new person. Good luck!

I would pray over this & I would enlist the choir director's help in either moving your seat or approaching her.
If her breath is as offensive as it sounds she probably has a gum infection that is a serious threat to her health. So advising her might risk her feeling embarrassed but could literally save her life.

Odds are if it's persistant she has gum disease, which she may or may not be aware of. If she is aware, it's likely she hasn't solved the problem to the cost of the procedure to fix it. (it's scary expensive). I would just politely ask to be moved to a different seat and let it be someone else's problem.

Send her an annonymous letter. My boss has done that before for clients that, due to age or illness, are lacking in the "fresh and clean" department. This way they are made aware of the problem without embarassment on either side. The letter would be from a social friend and honestly written, or typed, to get the point across. It has always worked.

No one has told her because there is no polite way to do this. I would suggest the breath mints, as well. Pop one in yourself and then offer one to her. If she says no, you're out of luck. Perhaps you could move positions? Good luck!