Too unrealistic, its obvious she would use her liquid assets (and if she really has none, liquidate something she owns, or loan some with a fixed sum of her inheritance as guarantee (no debt hell for her, no!). Hell, later on she lost organs to the doll, which she could have sold instead to get said liquid assets) to exchange for the lowest coinage she could get her hands on, possibly even other currencies. Or better yet, find something where each unit is even cheaper (rice, perhaps?)! Then she could easily sustain it forever.
Most of all tho, its unrealistic cause the butler could at any time have given her whatever. I am sure that he could sacrifice a grain of rice out of his own salary, each day, just to ensure he gets to keep his job. Or if he really is that cheap, she could have snuck a bit of her food to the doll, each day.