Talk to your advisor about this girl following you around because of a crush. Seriously - rejected people can sometimes be problematic, so you want that out there to an impartial third party authority at your school.
Now, as for your 'pal', you need to, in public, tell her that the two of you are not friends. I say public because you want witnesses. You do not want to give her a means of having a private emotional outlet. If she wants to cry or scream about it, then it's in public. Be firm, direct, and clear.
"___(whatever her name is), we are not friends. We never have been. Leave me alone."
Then leave. Period. Do not wait, do not listen, do not offer an apology. Just go.
Now, unless your classes are very small ones (and as a freshman that is less likely, albeit not impossible, particularly if your school is not very big), then the main thing is to sit somewhere away from her and surround yourself with other people. Possibly even go so far as to get in early to grab a seat or late to be forced to grab one elsewhere. If she 'saves' you a seat, don't take it. Just, avoid proximity.
After class, you are busy. Make up something if you must. You work off campus. You are going on a field trip. You have to study at the library and you work best alone. You're going on a date. Whatever. If you don't want to out and out lie (and you don't owe this gal the truth, BTW), then use the studying excuse. After all, you really do have to study at some point.
You are always busy.
Make friends in class who are not her, whoever they are.
Hence a part of you always being busy is that no one on one time with you is possible for her.
If she begins to give you other forms of grief, e. g. visiting your dorm too much, changing seats in class to sit closer to you, accosting you on the sidewalk or the campus bus or whatever, then start with the regular channels. Problems in class? Talk to the professor. Problems at the dorm? Talk to whoever is the head of security there. Problems on the bus or sidewalk? You can escalate it to the campus police.
All the while, as I mentioned first, if you have already talked to your advisor then there is already a record of complaints. And keep a record, too, as detailed as you can make it. I'm not kidding, because if it gets really bad and there is a disciplinary hearing to see if she should be kicked out of the school, that information will be valuable.
And hang in there. I'm sorry this is coloring your experience, and she is a jerk of the highest order and utterly clueless if she thinks this will somehow get you two closer. The whole things sounds a lot like a rejected suitor which is why I am urging caution.
But don't let this run your collegiate life, and don't feel the need to transfer or the like unless it gets really, really bad. Maybe keep your plans to yourself, too, e. g. when it comes time to select your classes for the spring semester of 2016, don't tell anyone which classes you are taking.
If she gets violent, of course, then call 911 and the regular cops, campus cops be damned. In the meantime, I hope she finds other interests and finally gets the message that you are not interested.