You have two choices. The first is to stop paying support and respond to any attempts to collect it with the defense that your husband's daughter has reached the age of majority and your support obligation should be canceled. You may be on the hook for the time between when you stop and when she turns 19, but at least you put the burden on your husband's ex to prove a right to the support.

As a practical matter, you might use this as an opportunity to save some money by putting the support you would have paid in an interest bearing account. That way, if you are ever ordered to pay the support, you will be able to put your hands on it.

Your other choice is to go to court in Wyoming to amend the order to relieve you of support on the ground the aging teen is now 18.