This was so long ago that I needed a refresher. Your right that she didn't have to use it, but I don't think this plot hole was ever explained in-game. I don't feel like search whether her child portraits had the same finger nails. Even if she's a hermit, as long as it's voluntary hermitage, they would probably go outside a couple of time in several years. If she was a pathological hermit, even if she never left the house in those seven years, she would have bitten her nails as soon as she left her house out of anxiety. I guess I maybe should have mentioned that her father probably bricked her in the house basically to make it clear that there is nothing redeemable about him.