She may know already, there are conditions that can cause worse than normal body odour; I have a friend who has it. Sometimes they have expensive botox injections that offer some relief. All the best with it, I hope she appreciates your being candid, after the initial shock. Be prepared that she may be upset and initially react in a way that's not considered.

If you're a good friend and you can tell her kindly, then absolutely.

I found this article...tell her! [kiddy.org.uk]

Tackling it head-on is the kindest thing you can do. If the roles were reversed, what would you want to happen?

There is no polite way to say it. Do you care more about what she will think afterwards or helping her? Unfortunately, usually the person with bad body odor is the last one to know. One more comment, I doubt an industrial deodorant is the answer. Maybe something as simple as a daily 5 min shower?

First - you might need to determine the source ...

I agree you should say something if you are good friends. A way to try avoid the words “you smell bad” or “you have body odor” might be to say I feel like as a friend I need to tell you, “your deodorant doesn’t work.”

As her friend, it might be a bit embarrassing, but believe me, you guys will laugh about it later. You have to tell her. I am grateful to a friend of mine who told me a similar thing about my breath. Turned out I had some sort of bacterial thing that was easily fixed, but I had no idea my breath was that bad. Tell her you will be her volunteer odor detector and make it a little fun secret between you both. Sniff her up like a dog before she goes out...lol...

Has she asked anyone of your circle about the ghosting? That would be the perfect opening.