Tele, here's something that hasn't been brought up yet.
Ok, you want your 18-year-old spouse to dismiss her father's wishes -- who clearly doesn't want her dating you. To this end, you quote Church teaching, St. Thomas, etc.
But you're really missing a vital point here: If you want her to (respectfully, I hope!) disobey her father to follow the "higher path" of pursuing marriage with you, you'd BETTER be REALLY well established, because you'll need to pay for an apartment for her to live in until you're married!
Long story short: Even if a woman can oppose her father in certain cases, she most certainly can't while she's under his roof. Children must not only respect their parents, but obey them as well, while they still live under their roof. She is welcome to leave home at 18, and then do whatever she wants.
If she is "of age" according to the Church, that just PROVES what I'm saying. A person "of age" is only living with their parents for their own convenience, and there is a certain contract between them and their parents. It is just that the father who provides for his 19-year-old physically gets a bit more say over that (adult) child's life than if she were on her own.
You think to think about that one for a few minutes, deeply. How could she (or any woman) oppose her father on a daily basis, while telling him, "Oh, and I'm going to live here, and you'll keep feeding and clothing me." Sorry; it doesn't work that way. You don't get some kind of "best of both worlds" where you're an adult as regards obedience, but a child as regards who supports you.
Matthew