Usually it's fine to just have the heating on for a few hours a day, though, then the house cools down slowly. By then everyone's warmed up and so it should be a while before you need the heating on again. Nobody's incapable of putting a few more layers of clothing on, and nobody needs the heating on 24/7. If you have the kind of special needs that chocoholic describes, then frankly you should be living in a place where those needs can be catered for (e.g. halls, where heating is often included in the rent), rather than making others pay for your needs (assuming those needs produce a ridiculous excess, as it appears in the situation the OP describes).
OP - suggest having the heating on for just 4 hours a day or so. Failing that, threaten Mini-Heater Girl with the prospect of her paying ALL of the charges incurred by said mini heater.