The rule of thumb is that babies usually double their birth weight by the age of 4 months, and triple it by the time they become 1 year of age. As of the age of 4 months, the rate of weight gain slows down a bit, from 900 grams per month to about 600 grams per month.
But you need to know that not all babies grow at the same exact rate and they usually follow their own pace. Your baby may gain weight faster or slower than the rates mentioned above, and a rate of weight gain of 0.5 KG per month is acceptable. The birth weight also affects the rate of weight gain during the 1st year of life. Also, babies go through growth spurts and fluctuations in their rate of weight gain. Therefore, your baby might not remain at the same percentile for weight or height every time the doctor takes her measures.
But on average she should maintain her growth percentiles at more or less steady values with intermittent fluctuations. Check her health record for these values to be reassured.