With her being that small at birth I think she is doing wonderfully! She will be small at least for a while due to being so early but if she is proportioned well height to weight than I wouldn't worry as long as she is on her own curve that just falls below normal on a regular curve. You have to keep in mind that in the birth section she was far below the chart...that is where her curve starts. If she has gotten back on the charts already after starting out that small I am excited for her. Check her growth chart and as long as she stays on a curve similar in shape/pattern to that of the lines I wouldn't worry at all... If she has flat lines all over the place I would worry but if she has a steady curve I wouldn't worry.