Army regulation for officerenlisted dating
This means that a member of the military who has sex with a person under the age of 16 is committing a crime.
Depending on whether the sex is consensual or not, the crime can be punishable by death.
Generally, the UCMJ will not charge a soldier with adultery if the person who is married, happens to be separated. Relationships between Soldiers of different rank are prohibited if they— (1) Compromise, or appear to compromise, the integrity of supervisory authority or the chain of command.
You could speak with the sailor's commanding officer and perhaps ask them to discourage the relationship.
There really isn't much that the Navy will do in regards to the sailor dating your daughter.
However, the UCMJ will charge the soldier if the involvement begins to interfere with the soldier's performance or if the relationship brings discredit to the service. (2) Cause actual or perceived partiality or unfairness.
If the soldier's relationship doesn't affect the routine and doesn't bring negative attention to the military, usually, no action will be taken. (3) Involve, or appear to involve, the improper use of rank or position for personal gain.