First, are you sure the ticket is just a ticket? Officers do issue tickets for criminal charges, as well as civil ordinance violations. Trust me, it is easy to make this mistake; and I know many others who have. I would not have to ask if it had not happened before.
Second, what is the prosecuting agency? Is it the State of Wisconsin, or a city, town, village, etc.?
Regardless of the answers to the above questions, you are always infinitely better off pleading Not Guilty initially. After you plead Not Guilty, a pretrial date will likely be set. At the pretrial, you can discuss the case with the prosecutor; and this is when the prosecutor makes an offer to resolve the case short of trial. In other words, the pretrial is how you get the most money knocked off.
Pleading Not Guilty initially does not mean you cannot change your plea to Guilty or No Contest later. Pleading Not Guilty initially simply means you want to discuss your case with the prosecutor.
I strongly urge you, however, to consult with an attorney. College students may be denied federal and/or private student aid for drug-related convictions. If your girlfriend's ticket is truly a civil ordinance violation, then she may be safe. But, she should not take the chance. Most initial consults are free, and there is likely an attorney who can address her financial aid concerns quickly and without charging.
Finally, if your girlfriend insists on pleading Guilty or No Contest, then she should plead No Contest. Guilty accepts responsiblity for the offense. No Contest means you maintain your innocence, but believe the prosecutor can make its case against you. A No Contest plea may help your girlfriend if her student aid gets pulled. A Guilty plea would not.
Hope this helps, and good luck!