My 18 months old is at 9kg and this was her weight since 6 months old. Is this something I should be worried about? She is eating well and growing well just no weight increase.

It is common for babies to slowdown in terms of weight gain at around 6 months of age. This is due to the increase in their physical activities. As long as your child is eating well and meeting the developmental milestones, her lack of weight gain shouldn't be a cause of concern. You could check with your doctor to put your mind at ease.