Goodness! Well, I completely empathize with you here.
I think Joe & Gina have some *very* good advice, but I know - if I were me in your shoes - I'd have about had it with "Susie" and would probably be itching for some uber-clever nugget of wisdom to shut her mouth once and for all. In truth, I've recently felt that I've about had it with co-workers (and some family) of my own.
I agree with Joe, however, that any attempt to educate every ignorant know-it-all around you is probably already a lost battle. It's one I had a tough enough time winning against myself, actually. When, from my ICU bed emerging from a near-coma and coming down from a 1600 blood sugar, I first heard the word, "diabetic" come out of my doctor's mouth, I was livid. And I immediately thought of my aunt, who had been diagnosed with Type 2 just a few months earlier. I was incredulous. My aunt is overweight, alone, inactive and just - well, sad & ugly (speaking to her character, mostly). Recalling all the overbearing narrow-mindedness, rudeness, possessiveness and jealousy that had always embodied her attempts at being close to me, I remember thinking to myself, "I cannot possibly have THIS in common with her!" It was a nightmare.
Needless to say, I bombarded my doctor (who I didn't know at all until that moment, actually, because my primary care physician, who *should* have noticed my symptoms but didn't, had deferred to this doctor - an endocrinologist - in the ER) with a powerhouse of accusatory questions, like, "How does a person leave a doctor being told she should just 'live it up' or 'go have a banana split' to gain some weight back... and then end up a diabetic in the ER?" It didn't make any sense to me. But I very quickly - very happily - learned that it was NOT the same disease with which my aunt was dealing. (And, in fact, she's not been taking care of herself very well at all since she was diagnosed with Type 2.)
It does seem strange to me that any person with Type 2 would claim to have anything at all to teach someone with Type 1. Type 1 -on its own- clearly is a more serious condition; I will admit, however, that most people I know with Type 2 unfortunately seem to have other health problems they complicating matters.
At the end of the day, though, a healthy diet for a Type 1 diabetic looks the same as a healthy diet for ANYONE. And if I'm going to judge myself for eating more ice cream than I feel I should have... then that's MY business... not anyone else's.
That said, if it bothers you, I think you should say something. I'm not very good at being tactful all the time myself, so I know how tempting it must be for you to put her in her place. But maybe you can take a look at Gina's etiquette card and find something you can use. It does make some good points. Or maybe you could just pull "Susie" aside some time and tell her plainly, "Look. I know we both have diabetes. But yours is Type 2 and mine is Type 1. And if you've read anything at all about either of those, you'll understand how tremendously different they are. I don't presume to offer you advice or criticism about your condition or how you handle it... and so I'd like the same respect from you toward my own condition." And if that doesn't work, maybe you could just threaten her with an harrassment or 'hostile work environment' complaint. ;o)
Please let me know what happens with this. I could use some advice myself.