Fat doesn't make you fat! It's a huge misconception people have.
And healthy fats are great for you, like the fats you find in fish, omega 3, etc.
It's not as if she's just eating straight trans fats, which are the unhealthy ones.
Protein is great for you too, it helps repair muscles after a good work out
A lot of people have this 'Atkins is unhealthy' stigma that they can't get passed. When I first heard about it I was the same, and I scoffed at the idea of counting carbs. When I got into weight lifting I realized I had to cut my carbs down a ton and couldn't get control of it.
Atkins has helped me learn how to count carbs. After doing a lot of reading, it makes sense. I even explained how it works to my fiance and he said 'That sounds like a really smart way to lose weight'
The sucky thing about Atkins is because so many people have that stigma about it, it get's a bad rap. Maybe she could just say 'A lot of people have the misconception that fat makes you fat, which is completely wrong. They also don't understand Atkins from what they've heard from others. I suggest you do some reading on it.' And then leave it at that.
It's just something we have to deal with. There's always different people mocking different diets. I mock VLC diets myself, because I think 500 calories a day is ridiculous, same with a certian diet we can't discuss that involves injections. I have a friend on it, it works for her, but I don't think it's safe personally. I don't say anything negative to her though because I am polite unlike your friends co workers