Emma's niece would have had to lease it to Red and Dale for 1 year I believe in order to keep the Miley's out. After that year the first right of refusal would have been null and void, then she could have sold it to Red and Dale the next year. Or she had to let the track sit for a year, I forget. Regardless, I assume she wanted the money ASAP and didn't care about racing or Nick and Emma's legacy either.
If I remember correctly, the lease said that the Miley's would have to maintain the facilities, in the same condition, as when the lease started, they hadn't, so it would have cost them a fortune, in repairs/compensation. So, they decided to buy it, thereby using the money they would have spent, to bid against Red. In retrospect, the track's fate was sealed, then and there.