If she'll eat eggs, you can do a lot with them - boiled eggs (plain or deviled), egg salad, egg over rice, egg custard, etc.
Cheese is also pretty versatile. Think outside the box and melt it over rice, instead of pasta. Add a scrambled egg to that and it becomes an even better meal.
Will she eat beans? Beans and rice is a favorite of many older people. Cook the beans a long time, to reduce unpleasant side-effects.
If she'll drink smoothies, you can add yogurt for protein. One of my favorites is vanilla or strawberry Greek yogurt, with a banana (mixed in blender).