A kitten gains about a pound per month, so if she's 3 months old, she's right on target for her weight. Now, if she was only 1.5-2 pounds and was 3 months old, I'd be concerned. I don't think you have anything to worry about. I know that my male cat is larger than my females. I think that's just how nature works. Males in most species are larger than females. She is also big enough to be spayed now. Pediatric spays can be done at 2 months or 2 pounds.
I currently have 4 adult cats and the females all weigh in the 7.5 - 8 lb range. My male, who is much longer and bigger, weighs about 11 pounds.
I currently have 4 adult cats and the females all weigh in the 7.5 - 8 lb range. My male, who is much longer and bigger, weighs about 11 pounds.