15 month old hasn't grown in 6 months

My daughter was born 9lbs 22 inches. She was in the 100th percentile for a long time but slowly started going down. She kept in the 90th until she was 9 months old then she basically stopped growing. She is currently 29 1/2 in tall (the same as she was when she was 9 months) She also weighs the same as she did when she was 9 months but is currently in the 70th percentile so I'm not as concerned. I brought it up to her doctor but they brushed it off. I know babies start to even out but it seems like a big drop to me.