I almost worried you were my husband until you said "married for 10 years". You basically described my life and I have suffered from bulimia for 11 years.

As far as how to approach the topic. I am not sure there is a polite way to do it. Chances are she will deny everything and possibly become aggressive when asked if she binges and/or purges. If she doesn't want help, there isn't much you can do. Although, if you are able to catch her purging, that may be a step towards getting her to admit it. Eating disorders usually have a very strong grip on the sufferer and provide a huge sense of shame/comfort as a coping mechanism.

I am not sure if I was any help, but I hope she opens up to you and seeks treatment.