She looks a little "fluffy" but not bad. I would stick to the three week feeding schedule and handle as much as possible when the snake isn't digesting or in shed.
During the winter my three year old and older boas go on half rations but on the same feeding frequency. So, if they were getting a large rat every four weeks, they get a medium, or something like a rabbit fuzzy or older chick that weighs around 100 grams.