Is it normal for a female budgie to eat the sandpaper at the bottom of her cage?

Most seed eating birds require grit of some form in their diet. It is used in their gizzard to grind against the seeds to break them down. If no other grit is available to your bird she is using the sand from the sand paper for the same purpose. Female birds alo need a source of Calcium in order to make shells for their eggs. Cuttlefish bone is commonly hung up in the cage for this purpose.