Well... I actually read your post the day you posted it. But I didn't reply because I didn't think there was much of anything, of any consequence, I could offer. That may well still be the case. However since no one has yet replied to your post, I thought I'd take a swing at it, so to speak. (Hope you're still around to read my reply.)

Given what little I know of the whole situation you describe, since you know your father is "turbulent" & "relies heavily on instinct", my inclination would have been to try to simply say something as neutral as possible. (I really dislike confrontation!) I'd have probably gone with something like: "She seems nice. But what's important is how you feel about her. If you're happy... then I'm happy." As my father used to say, many years ago, "discretion is the better part of valor..."

I was struck by your mention that your mom is taking you to a psychiatrist as a result of this occurrence. To me that seems like an extreme reaction. I don't know how things work where you live. But where I live, all most psychiatrists do is to prescribe & monitor psychiatric medications. In order to talk about mental-health-related concerns, a person would typically see a mental health therapist, or in some cases perhaps, a psychologist. I'm certainly no expert with regard to these sorts of things, but what you described just sounds to me like a pretty normal family dispute between a parent & a young adult... not something that should result in a trip to a psychiatrist's office. But perhaps there's more to this than you could write in your post. Under any circumstances, I wish you well...