When you tell her "you're not going to get a job from Charlotte School of Law" she's hearing "I don't have faith in your abilities." She doesn't believe you when you tell her most people from Charlotte School of Law won't get jobs as lawyers--that runs counter to the common narrative about law school.
Couch your argument, instead, as about not wanting her to settle. Tell her it's a choice between any old legal career, and a top legal career. Point out how many fancy lawyers went to UNC and how no matter how great you are it always helps to get a head start by going to a brand-name school. Convince her of your faith in her ability to do better and your disappointment in her deciding to settle. Pandering with a touch of guilt is going to get you much further than just laying the facts out.
If your wife needs to be coddled, then I expect her to struggle as an attorney.
Sack up and say it's not happening. If you can't veto spending this much money on something, then that says more about you and your relationship than your wife. It's only going to happen if you allow it to happen. And then don't complain to anyone, especially anyone here.
I mean, can she just go out a buy a home without your consent, too?
You have to pick and choose your battles in a relationship. This is one you should be ready to fight over.
AFTER the fight (and there will be one), talk with her about test-prep courses.
If she struggles so much with the test, then I would encourage that you sign her up for a test-prep course. While many people on these forums feel that it's a waste of money, it will most likely do wonders for your wife (not Kaplan). That way you know that she has done reasonable prep and if she still scores low, then you guys can reevaluate at that time about realistic prospects. Plus if you sign her up and "invest" the course fees into your wife, you might be able to pull off some sick makeup sex.
(Seriously, I highly encourage a test-prep course or a tutor in this case. If she put in effort and stuggled to get a 150, she is not seeing the logic / learning tactics that WILL add points to her score.)