Can the promoter of the first concert legally force her to honor her contract?

As of the date of your question, it would be impossible to force the performer to sing as the date has already come to pass (assuming that the concert was for December 24, 2011, and not a future date).  As such, specific performance of the contract is not an option.  You may be entitled to damages for breach of contract, and should contact a local attorney to determine whether it would be worth filing suit. This is not intended to be legal advice, and is general in its nature. No attorney-client relationship exists or is formed by this information. Furthermore, this does not represent the views or opinions of LexisNexis or its affiliated companies.