It is usually not a good idea to give your tenant an option to buy the property unless you plan to be a long-term landlord. Remember, you originally planned to flip that house. The only reason you even have a tenant is because something did not work out the way you planned. Technically, the presence of a tenant is an obstacle to selling the property to someone who wants to live there. While you can potentially sell to an investor, if the tenant has a contract with a purchase option, no investor is going to be interested except at a very deep discount.
On the other hand, if you and your lender are reconciled to being landlords for a year or more, then a lease option might be a good idea. The strategy has a name and is called the grow your own buyer plan. If the person can afford it, the best prospect to buy a house is almost always going to be the person living in it as a tenant. Just make sure you do not have another flipper for a tenant. That person will tie up your property with his or her purchase option, but only exercise the option if they can make a profit on a quick resale.