Congratulations to your daughter for spreading her wings. If the move is temporary, such as school, she may be able to remain a tax dependent on your return and remain on your policy. However, there may not be any out of state network providers depending on the plan. https://www.healthcare.gov/income-an...ousehold-size/
Otherwise, you will need to report the change to your state/federal health insurance exchange. The current policy will be cancelled and a new policy issued reflecting a premium for the remaining two enrollees. A family of two earning less than roughly $63,700 can still qualify for a premium subsidy. The new subsidy, if any, will be based on the new family size and new premium for the remainder of the year.
If she is no longer a dependent, a portion of the January-August subsidy actually belongs to your daughter. In most cases, the parents will just keep the entire subsidy but you do have to report that decision. See Instructions for Form 8962
, Table 3, Step 3 for more information.