Awww she's gorgeous - don't be sad that she's getting bigger, it's lovely watching them change. My daughter is 4 now but she was like Riley at that age, as soon as she started to get active with crawling, bouncing, cruising and walking she lost the chunkiness.
Do you have a red book for Riley, in there are centile charts, u plot in the weight against the age and see where she is against the average line/heavy line/light line.