My 7yo daughter fell from her bicycle last week and simply refuses to get on again. How do I convince her that it's okay to ride the bike again?

Right now your kid is still a little shocked and scared. To you right now it must seem as a small incident but waith a few more days. Give him a morale boost that he is growing up and such incidents are a part and parcel of growing into a tough boy. Encourage him and tell him you are there to help him when he gets onto the bike again. You could also share an incident from your childhood when you were learning to ride a bike. Make it interesting and funny for his benefit. :)