Assuming that there are no allergies at work here, where certain foods make her feel bad, and there are no sensory aversions where certain textures are unappealing, then there is no reason to live on that limited a diet. While all kids go through their picky eater stage, it is very often an issue of asserting control. If you set yourself up for a power struggle, this stage will last much longer than it needs to.
My advice would be to give her something she enjoys for two of the meals each day, and give her something new to try for the third. Either she eats the new food, or she doesn't. You can even offer a choice of two things outside of her comfort zone, and let her choose which to try, if it is hard to just put something in front of her. Once she tries something a few times, if she truly dislikes it, then don't force that food on her.
We are hardline in my house with food issues. I won't make you something I know you really dislike. But, that said, I make one meal, you eat or you don't. My son eats like a champ, reasonably anything but peas and broccoli, which he has disliked in all forms from baby food jars till now.