As hard as this is going to be, leave it alone! She knows what he's like, she's embarrassed about it. So that's good. The more you criticize him, the more loyal she will be. She's a driven and accomplished young woman, and she is smart. She sees this. She may be the caretaker type, unwilling to cast aside a needy human - it may or may not be the same emotion that makes her want to help helpless animals. So the harder you push, the more you drive her to him. She may also be dating him because he's easy! He's not driven like she is, he's always available when she's done studying, he's not high maintenance. She may like the companionship especially knowing she doesn't have to do much to hold on to him right now. With her studies and her workload, the old and familiar may just be easier for the time being.
But she's not slacking in her studies, she's not imitating him by lazing around the house - just the opposite. So I think that's a good sign.
Sometimes people don't want to have their parents say "I told you so" - I dated a guy in high school that my parents didn't like because a) I had low self-esteem and he paid attention to me, treating me well, b) he was cool because he was in a band, c) my parents (especially my mother) didn't like him and I didn't want her to be right about this. So I stuck it out just so I didn't have to face her.
The best thing you can do is be a loving and supportive parent, and to continue to praise her for all she accomplishes. Focus on the drive that got her a job where there were no openings. Praise her good grades. She's got a lot of school ahead of her if she's 19 and wants to be a vet.
Do not be mean to the boyfriend - be polite and then some. Do not engage with the boy's parents - they have no backbone or they think they are helping their kids, but you will get nowhere if you critique their parenting. They may even take it out on your daughter, saying something along the lines of, "Well I know your parents don't approve of our methods, but you don't agree with them, do you?" She will have no choice but to stick around and back him (and them) up.
I don't know why you think her future husband will have to provide for her financially - she's obviously going to be quite capable in that area! I think, in time, her career objectives will be matched by her maturity and confidence, and she will see for herself that this guy will hold her back. She's got quite a few more years, and he has time to either find a skill or a profession, get a fire in his belly, or be left behind by her.
You call her a grown woman, and legally she is, and I know some people in your family have gotten married at that age. But she's still young in many ways, and inexperienced. If she weren't still young, you wouldn't be so worried about exerting more control and influence over her.
As she spends a few more years in school, looks at money (jobs, school loans, whatever), and learns to live on a budget, she will see that she's going to have to pay the freight on this boyfriend. He will become more diminished in his own eyes as her education increases, and if he doesn't straighten up, she'll move on. She'll be stronger for it if she learns that she can have a career and depend on herself financially, and not need a man to pay the bills. That's entirely different from wanting to pay the man's bills!
Let it run its course. So many high school romances don't survive college. Don't panic. Let her grow up on her own, with your support. If you belittle her choices, it will undermine her self-confidence and her willingness to move on to a life with no man or with another man.
The hardest thing for you and your husband will be to hold back and stop worrying. But it's the most important thing you can do to enable her to move in the right direction.