Very few babies will perfectly follow the percentile lines every time they're weighed. As long as they're gaining weight, HV's don't usually worry as long as they're not consistently dropping down the chart. Lots of things can make a reasonably big difference to their weight when they're still quite small - just having had a feed or a very heavy nappy, even a different set of scales can make a difference of a few ounces (just having them weighed at a different time of day can change their weight).
You'll probably find that next time you have her weighed in a couple of weeks she'll have gained a normal amount again so until then - as long as she's feeding ok and you're having lots of wet and dirty nappies - I wouldn't worry x