So first, the only opinion that really matters here is yours. If 100 people here say it's fine, and you still can't get past it, then you need to break up with her.
That said, if I were in your shoes, I would figure out the "why," because that's what speaks to the important things about her character and priorities. Did she make a well-reasoned decision to pursue a career with six-figure possibilities, did the debt reflect what she had to spend given the options available to her, and does she have a plan to pay that debt off quickly? Or maybe did she make decisions at 17 or 18 that she now recognizes were mistakes -- the wrong college degree causing additional post-graduate costs, an expensive college because her parents told her not to worry about the money, etc. -- and she has learned from those experiences? Or maybe she was completely frivolous and bought a lot of fancy/unnecessary stuff with that money, and has now realized how stupid that was and regrets how much those decisions interfere with her real plans and dreams?
All of those people are very different people than someone who blithely chose schools regardless of cost or career, took out as much as someone would lend her and spent every penny, and wonders why you're making such a big deal about it since "everyone" has debt. Which one is your GF?
That is why people are saying don't focus on the money: because in the end, what matters is not the money itself, but what the money says about the person who owes it. Right now, $200K sounds like a huge amount of money. And I don't want to belittle that, because you are right, it will affect what you can do for your first few years of married life. But over a 50+ year marriage? It's nothing -- it's just an annoyance that you can blast out of the way in the first few years and then tell stories to your grandkids about how tight things were when you were young. What matters far, far more is whether you and your GF currently share the same values and dreams and priorities. Because like
@terran said: in the long term, you will wind up far better-off financially with a Mustachian who starts off $200K in the hole than you will with a non-Mustachian who starts off with $200K in assets.
Trust me on that, as I married the latter (high-earner, high-spender). And I will tell you, despite the giant firehose of cash that came pouring in, we
still had arguments about money. How is that possible? Because we disagreed about what we should do with that money. That's why the people who say most marriages break up over money are wrong. The truth is that most people break up because they disagree about what to
do with money -- and then cannot communicate effectively, and so never figure out how to reach compromises that make both partners happy.*
Sure, there are some people who are truly poor, can't climb out of debt, and break up simply over the constant stress of never having enough. But that's not you. With your GF making $100K, you will have more than enough to pay your bills, pay the debts, and still save, even if you don't bring in any money at all. And that means that this isn't a money issue -- this is a goals-and-priorities-and-communication issue. So talk to your GF and figure out if you are closely-enough aligned in what really matters to build the kind of future both of you want, on a timeframe that you can both be happy with.
*We still disagree on the money bit, but we at least managed the communication and compromise stuff well enough to make it 23 years and counting.