I'll preface this with that this is an issue I'm sensitive about (particularly after a very frustrating visit to an endocrinologist), so I might be reading too much into your post...

It seems to me like this post is VERY full of judgment for which you have absolutely no basis. It's possible that the "macaroni and cheese" was a special occasion food for her (it WAS a holiday luncheon), and not what she normally eats. Not sure what was wrong with her salad (other than, but for the cheese, greens usually aren't unhealthy). You have no idea what she does or doesn't want to do (heck, she might make herself cook healthy food, but not like to), or what might be the source of her weight problem. You also have no idea what causes her joint issues.

I'll grant you that most people don't know what healthy food looks like, and are absolutely not willing to put in the time to make sure they eat healthily or exercise. But - that's not 100% true. I cook extremely healthy food most of the time. I occasionally splurge. I have a weight problem. I have seen nutritionists with food logs, and MD's with exercise logs. I do have a thyroid problem that is still an issue and is likely part of the problem. I am so tired of people rolling their eyes at me the one time in a week or 2 that I might have a small frozen yogurt, or some other splurge. They judge, and it's not appreciated. They don't have all of the information, and yet they feel free to pass judgment and sometimes make comments. Please, please think about the judgments you are making. While it's certainly unlikely your coworker reads TE, I bet that some of your judgments come across in your interactions with her.

Start a discussion of the time required to cook and eat healthily (and exercise) if you want - heck, I'd love some lunch suggestions that pack easily. But, please, please don't judge another person to make your point. It's not necessary, and it might be hurtful.