My little man hovers in the 5th percentile on the charts... what my pedi said was not to worry, since his growth pattern follows a nice curve.
A few things to consider are the fact that your daughter was recently a bit ill, which attributes to that little dip in wt. I'm sure she's hitting some milestones right now that would contribute as well (teething, etc.)
Try not to stress just yet, as that can affect your supply. Give it a bit more time and a careful eye before being overly concerned.
Wish you well!