Hi Karina
First it is not a ridiculously dumb question.
6 to 8 wet nappies in a day is good. This tells me that your baby is getting enough fluids and therefore is having enough to eat.
When you express milk you will never be able get a much as your baby can. Depending on how hungry she I she will get somewhere between 100 and 180mls per feed. If you want to express milk it is a good idea to express after feeding your baby. You can freeze this milk and save for situations like you said.
If you are only expressing 30 or so mils then you could put this into ice trays and freeze it that way. Or you can add fresh breast milk to previously frozen milk providing that the fresh milk has been left to cool in the fridge for 2 hours.