What you feed your kids is up to YOU (and hubby). She has no place to say anything to you about it...unless it was actually causing a problem, then I could see her sharing a concern constructively. And, I'm not a fan of low fat anyway! I mean, bad fat should be avoided, but there's more and more info out there as to how important fat is for us!
As for bridging the gap, I have no suggestions. What you described sounds similar to my MIL, only my MIL is born and bred USA and still doesn't get jokes and is so easily offended and is the constant victim. I've tried hard, but I've had to come to accept that some people choose to be the way they are, and there is nothing we can do about it. I can only control myself. So, I work on that. I will treat her well, but I also won't be abused by her, so I am not a pushover around her. But I think at times there is nothing you can do to bridge the gap. That takes two people, and you can't do it unless she's interested too. I've tried bridging the gap with my MIL. I've even apologized for anything I might have done to offend her, but she wasn't interested (and I should add, she's way more offensive than I ever have been! She regularly ruins relationships because of her attitude/personality being so selfish and hurtful). Anyway...so that's my suggestion. You can control yourself. Maybe focus on that. She might never respond how you hope. It doesn't mean there is anything wrong with you, though. i've struggled with that a lot. I kept thinking I should do something different, try something different, approach it a different way, etc...nothign worked. I know I've done my best...I can't change her...just as you can't change your MIL. Though, your hubby needs to keep things between the two of you private!
Good luck!