I'm certainly no expert but I think as long as she is gaining, happy and have wet nappies, sounds like she is doing really well. Some are just slower than others I guess. Have you seen a MCHN/paed? Are they worried at all? Try not to stress too much, if bubbas all gained weight at exactly the same rate they would all be the same and it wouldn't be too interesting! My DD hasn't exactly been fast with weight gain either (she's nearly 13 months), but ahead in all her milestones - crawling at 5.5 months, walking before 10 etc. They just do things in their own time!