Brand new babies rarely fill a nappy - newborns fit babies for 1 month+ by which time they will fill them! If you're worried put a little cotton wool in. If there's pee on it (pampers crystals easily dry ALL wee 1St few days and may not deploy the stripe) she's peed.
I also had a panic due to the misleading "heavy" nappy thing abd was advised as above by the mw. Now at 7 weeks her nappies are HEAVY.