Move 18yo YW back to YW

I have a young woman who is 18 years old and still in High School. The system has kicked her out of her YW class and now places her in Relief society. Can you tell me the process to get her back into the YW org. until she leaves for college? She won't be out of High School until next spring.

Got to the member record. This can be done either through the Organizations list or through the Member list.
If using the Organizations list -

• Click Organizations from the LCR menu.
• Click Relief Society.
• Click the Members tab.

If using the Member list -

• Click Membership from the LCR menu.
• Click Member List.

From this point on it is the same whether using the Organizations list or the Membership list -

• Locate the member's name on the list.
• Click the member name.
• Click the View Member Profile button.
• Click the Callings/Classes tab.
• In the Class Assignments section click the edit icon (pencil) for the Relief Society.
• Under the Class column click the drop-down list box and select the class in the Young Women section.
• With the desired YW class selected then click the Save button.

Will I need to manually move the 18 yr olds into RS once they graduate?

I would expect so. LCR has no knowledge about what grade they are in High School or about graduation.