75 is good, and by the window is good, just make sure the sun doesn't shine directly on her because she won't be able to get away from it and that would be as bad or worse than being too cold. Tonight though, if she makes it that long, could be too cold, unless you keep your heater on. I just use a low wattage light bulb directly over the box they are in. Don't worry, she'll be able to sleep with the lights on.
The weight loss is from not eating for however long this has been going on. They eat a lot in their natural, healthy state, like constantly if they have the range available. So, instead of consuming what she has been eating, her body is consuming itself.
edited to add: I put the light bulb in one of those you would use for chicks that will reflect the light and heat downward.