You could try leaving her an anonymous note, I suppose.

I used to work with a guy who had the worst breath in the world. It truly smelled like an animal crawled into his mouth and died. You could smell it in the general area surrounding his office, too. And he was a guy who talked all the time, which made it worse. The strangest thing was his dad was a dentist. We always wondered why his family didn't try and help him. He was one of those people who needed to use a tongue brush and strong anti-bacterial mouthwash in addition to brushing his teeth.

We went to meetings and offered everyone at the table breath-freshening gum as the meetings started, which he usually turned down. Someone once left an anonymous tin of Altoids on his desk. When the ladies had to talk to him, we'd cover our noses with a handkerchief or tissue that had a drop of cologne on it. Finally one of our bosses had to tell him there was a problem. If it's disruptive to the workplace, a manager can do that. Everyone was hesitant to go into client meetings with the guy because he was so offensive. I guess the talk with our manager embarrassed him because he took another job not long after that. It was truly repulsive.

What's the smell of your colleague? Body odor like she doesn't use deodorant? Or just like she doesn't bathe or wash her clothes? When someone has an odor problem, that's not a good sign. Think about talking to your boss. There are ways to handle that situation diplomatically, but if it's disrupting your work and affecting others, she needs to know.