That's why MVPs were invented- define a minimum set of features and stick to the plan and get something out of the door, then build upon it. I find that some of the longest product-related discussions occur over features/edge cases that very few users may need/will seldom occur.
Agreed, you need to help her understand the value of an MVP given the fact that you are a single developer and I am assuming using spare time for this project. She has to understand that the project has to be broken down into small digestible parts if there is any chance of it getting off the ground.