It depends on the overall size and frame of the cat. Some would be overweight at 4.5kg whilst others would be underweight. Jaffa weighs about 4.8kg - he is a big cat (long and tall) but is small boned and quite a skinny cat (not skinny as in underweight, jut a naturally thin and lean cat). Mosi is about the same, I think, although he's not been weighed for ages and not since he stopped growing. He is a fairly large cat, although not as large as Jaffa. He looks chunkier than Jaffa because of his long fur, but there's not a lot of cat under the fluff.
The best way to tell is to feel around the abdomen - if there is more than a little bit of fat underneath the abdomen, she is probably overweight. You should be able to feel the ribs but not see them. If she is overweight, it will be easier to deal with when it's just a littel bit. Was she underweight when she was last weighed and found to be 3.85kg? I would be concerned at the putting on of weight unless she was underweight then and needed to put on some weight.
