Can you apply your knowledge of contract law principles in analyzing and interpreting this issue relating to contract law?

Situation:

Cheryl contracts to sell her moped to Jean for $900. However, a few days before Jean is supposed to pick up the moped, Cheryl phones to tell her that she has changed her mind and no longer wants to sell it. Jean is concerned, because to buy the same or similar moped elsewhere would cost at least $1,200. How would you characterize the breach committed by Cheryl? What remedies are available to Jean? If she claims damages, how would she calculate such damages? Would such damages be liquidated or unliquidated?