What kind of lawyer do I need? Real Estate, Contracts or Consumer or Consumer Fraud?

Daughter bought a brand new house from seller who is also the sales agent, developer, and lender. They are backing-out on a cash incentive that they promised. This initially seemed to be a small claims issue but after a couple of months of demands, they are now completely denying that there was such an incentive despite the agent's written commitment to it, which secured the buyer's agreement to the sale.