why does my house rabbit keep scraching the bottom of her cage?

It is natural for rabbits to dig and burrow. In the wild they live in burrows undergrownd that they dig for themselves. Make sure that your rabbit goes outside plenty somewhere she can dig into the ground. But make sure she doesn't dig her way out.

Most rabbits that do this are:

1- Bored

Simple, just give it a inside of a toilet paper roll with newspaper and hay in it.

2- Smell something of interest

Rabbits, especially bucks (males), will dig and scratch in the smell something new or different.

3- Might be food there

4- Rabbit might be irritated

5- Or it has long nails

It is a possibility that your rabbit is trying to file down it's nails by scratching something.

Rabbits like to burrow, it's instinctive.

rabbits were not invented to be kept in hutches.

they like to live in woods etc, and love to burrow. it's just doing what comes naturally.

that, or it's bored to tears.

they like to dig, give it some blankets, and shell be happy, my rabbits live theyre blankies

they love to dig for burrows

she is only trying to burrow, nothing to be alarmed about