N.M.
I wouldn't worry too much about it for now, since she's bound to get tired of it after awhile. The rule at our house, though, is that the children have to take one bite of whatever it is they don't want to eat. (Yesterday my daughter took her required bite and ended up eating a whole serving--she was surprised that she liked it!) A one-year-old won't be able to reason with you about the one bite, but maybe you can find a way to slip it in, even if it's while she's crying and having a fit about it. I think it will help her at least keep familiar with a variety of tastes while she's on the mac and cheese addiction. By the way, we always tell our kids "Thanks for trying your one bite!" very pleasantly, even if they were having a fit. And you might want to ask your pediatrician about a multivitamin to help make up any missing nutrition for now. Good luck!
After reading the other responses, I thought I'd better add a little more to this.... Of course, as a parent you are in charge of what your child eats, and if you want to enforce that she eats what you give her when she doesn't want to, you'll likely be in for a battle. Even if you are passive agressive (no yelling, just firm with your stance) with the "you'll eat this or nothing" strategy, it's still exhausting. (At least it was for me--we had many fierce food battles between about 1 and 3 years old.) If you can succeed with it, wonderful.
As for me, I finally decided that food wasn't an important enough battle to lose my sanity over. I wish I had relaxed a little about the issue sooner. Our policy now is that I make sure there is one thing on the dinner/lunch menu that the kids will eat (even if it's just the carrots), and with everything else we have the taste rule. Also if they don't finish the required amount of food, it waits for them (because you know they'll be hungry in an hour--that's their only choice until it's done).
It would be good if you can find a balance between making her eat what you put in front of her and letting her have total control over the menu. Even with your one-year-old, there must be some reasonable eating rules you can set with her. Best wishes with it.