Maybe it is my natal culture, which I suspect is related to but not exactly the same as NyaChan's, or maybe it is just my large, extended family, but it seems like all the living elders and many of the cousins, too, feel the need to know and comment on the minute details of everyone's life and deliver much unsolicited commentary and advice. They all use email and Skype, too, so there is no geographic cure.
When I married a man of another race, I was lucky because they all liked HIM, but they didn't like people LIKE him marrying in, sort of generally. Racist? You betcha. Normal for their ages and culture? Absolutely. It isn't hateful racism, like some people experience, but more a tribal thing, I think. Other people are fine -- they just aren't US. Mostly, they overlooked his extreme height and odd coloring <g> -- his language and social/cultural skills really helped -- and now they all seem to have entirely forgotten he is of another race and culture. He has become part of their "US" rather than part of "everybody who isn't US." But back then, I sure did get an earful, and not all of it arose out of genuine concern for my happiness.
What my mother told me was that the way this is normally handled in the Old Country is with rapt attention, deep respect, gratitude, and then doing exactly as you please. Don't push the issue, but don't take any of it to heart, either, IOW. Shalom in the home, as another old culture says. While that feels wrong to Americans, if that is the Old Country way, and that is the way to make the visits work, which it sounds like you have to do, without upsetting yourself, it might be worth a shot.
Could you try thinking, "Geez, Grandma is a toxic old blister" while saying, "Thank you for your concern and advice, Grandmother. I appreciate it and will give what you say serious thought." (For about a nanosecond.) If you speak it, using the Old Country language might help with the emotional disconnect. And then bean dip in a way that gets you out of her orbit? This is not something that is culturally approved in the US where life often strikes me as a therapy group, but it is certainly polite in the US and if your grandmother's culture is what I think it might be, it is both polite and normal there, far as I know, too. It is a cultural variant on "Not discussing this," but one she might understand.
And five or six pounds? Yes, that might push a small person up a size, but really! If that is all they can find to gripe about... Grandma IS a toxic old blister. Look after yourself, and don't take anything any of these people say seriously. Get out at the point where it starts to affect your emotional equilibrium! You have law school to finish, and that's more important than the Toxic Family's nonsense, for nonsense it truly is.