Agreements, or contracts, are enforceable; and furthermore, there is only the right to seek a refund IF the agreement itself allows or permits a refund. (Assuming, that is, that the work done was the work agreed to and was done to professional standards.) There is no right to change one's mind about an agreement, again, unless the agreement itself allows you to do this. Based on what you write, it would seem that she should have any right to get her insurance payments refunded, and, furthermore, should be liable for any remaining payments. If she will not pay voluntarily, you should be able to sue her for breach of contract.