Ahilash_Danie
Please don't be a Rias Simp. Even if you make her a normal teen, she has all the options and resources to get out of her arrange marriage if she actually put an effort. Besides they are on a medival culture with nobilty. Those stuff are normal and even then a thrid son of a leser house could only be the consort of the Gremory House, no real authority to egen force himself on the peerage or servants. He could do it by force but then that will cause real problems.