By the sound of things, your dad would have been difficult for her to be around. I think that getting on well with those around us is an admirable trait and I'm not sure I'd bother with someone who felt the need to challenge me like your dad did to your girlfriend.
I also wonder about him being hard on her due to her living at home. Where I live, housing and university are extortionately expensive and young people just can't afford to leave home till they have a substantial income. If you live in a similar economic climate, then perhaps there's a degree of her being sensible. Of course, you'd expect her to contribute to the running of the household and not have her mother waiting on her hand and foot
At the very least, you should expect both your parents to treat her with respect.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.