Until a child reaches sufficient size, strength, and mental desire/toughness, there is nothing you can do. Trying to start too early can put them off for life. If the first learning is that shotguns are not fun, you have made yourself a long, uphill battle. First learnings go really deep.
When the size and strength require a very small and very light gun, you may well be stuck with seriously reduced handloads or abusive recoil (abusive to the child - if she says it is uncomfortable, it is uncomfortable). Stick with what she finds fun to shoot until she grows into shotguns. Take care that your desire for her to shoot doesn't get interperted as a mandated to her.
Consider getting a cheap, used 28 gauge reloader and a few supplies. You may well discover that she enjoys reloading with you - many kids, under proper supervision, do enjoy it.
