Your first mistake was giving her access to your finances when she has proven untrustworthy with her own. If you knew she blew through 200,000 dollars in 18 months why would you give her access to your credit card?

I understand you wanted to provide her with some financial security but it seems you were too eager for another level of commitment without actually thinking things through or weighing the overall responsibility on both parties. From what you explained; you never gave her a numerical budget for the month. Sure saying "spend less, I'm trying to save money" is one thing, but you never explicitly told her "girlfriend you need to spend under 50$ every month for your expenses if we're sharing a credit card".

Your second mistake, aside from not capping a limit to her expenses; was not giving her a timeline to repay you. I'm getting the impression that she thinks she can spend whatever she wants and will just 'repay it later'. 4 years after you graduate? A month from now? Does she need to contribute to the minimum payments of the card at all? This whole situation is a shitstorm of irresponsibility on both parts.

Also, if you were the primary cardholder you should be indefinitely checking your statements. Which again, you wouldn't have to check line by line if your girlfriend could be trusted with a budget. You also should have capped additional cardholders with a spending limit. (Easily overrided with a call to the bank from the primary card holder)

You need to cut her off from your card and stop enabling her poor spending habits as she is clearly untrustworthy with money: her own and yours. You need to explain that her blowing your money was a breach of trust which is why you are removing her from the card. You need to set up a payment plan and stick to it. She should at the very least be contributing to the minimum payments. If not, take this as a very expensive lesson.