Copyright of a book?

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My mother wrote an educational book two years ago, which has since gone on to sell a few copies, and it turns out she doesn't have much in the way of a formal contract in place with the distributor.
It's been reprinted twice, and she gets a small annual cheque for a her share of the revenue. However, she hasn't received a copy of the agreement they signed at the outset, which she says was a one-pager that said she'd receive half of any profits after costs. Sounds generous, but what those costs are were not defined and they won't tell her how copies have sold or what costs were incurred.

Employment has de-facto contracts; if I pay you, you're automatically entitled to some protection under the law. Anybody know if authorship is similarly protected? The book is printed with Copyright (C) {the Publisher/Distributor}.

She really doesn't like conflict, and doesn't want to upset the Publisher, but I don't want to see her get screwed, and it seems like they may not be keeping things above board.

There's quite a decent default contract here; needless to say, she didn't ask them to sign a similar one, bless her sweet heart