How do you tell someone politely they smell?

I work at a gym, and recently we had a woman join a few days ago who just smells horrible! I have spoken to her a few times and is a really nice person. Then when she starts to work out she produces the most powerful body odor I have ever smelled in my life. She is European, and I know they are not accustomed to wearing deodorants, just perfumes, or sometimes nothing, but this is just way too bad. So bad that we have had several complaints about her from other members. People clear out the room because of her. My co-workers and I are stuck in this horrible situation we have never handled. I mean, we don’t want to hurt her feelings or embarrass her, yet other members are complaining and we have to do something about it. Should we tell her in person, write her an email, leave her a note with her gym bag with a complimentary deodorant? We also don’t want to offend her and then she decides to quit! Do you think she even notices that she smells? We also don’t want to make her feel like we are accusing her of something when she has no idea what she has done.
Any suggestions would be fine!! What would do, and what would you say?