My husband and I entered in a lease with the option to purchase at the end of the term. Our lease option clearly states we have 6 months after the expiration of the lease to exercise the option of purchase. If we do not exercise the option to purchase after the 6 months we forfeit our rights. Our lease expired at the end of May and our landlord is stating she will not honor the 6 month grace period even though we have the clause in our lease purchase contract. What are our rights regarding the contract with her?

You can file a lawsuit for specific performance. This is where she is forced to follow the terms of the contract. Send her a letter right now that you intend to exercise your option to purchase within the 6 month period. Send the letter by certified mail, return receipt requested, with another copy sent by regular mail. If she still refuses to sell to you then you can file the lawsuit to force her.

Yes, Lisa explained it well, you can enforce the terms of the agreement.