Conversation skills will require a bit of work in the long term. You will have to change the way you think about conversations whilst drilling a few techniques well enough to get you passed that lock-up point. I will post some links below for you to read through, they should provide more than enough material to spark something for a wide range of people and situation types. But more specifically to this girl: what observations have you made? Conversations are largely bolstered on observation, in terms of reading a person's body language, tone of voice all the way to being aware of your surroundings. What does she talk about? What do you know about her personally? Which class are you in? Do you interact outside of this class? Is she very talkative?
A real turning point for me was learning to ask questions. This one is very often the killer of conversations. Alot of people who struggle in conversations don't ask enough questions, which places the burden on the other participant to essentually mount what is a laboured interrogation. You don't have to be a motor-mouth to have great conversations. Finding a balance between answering and asking questions and making statements is the key. Write out some bullet points about this girls, trying approaching it from the perspective of curiosity in her. Learning to have a bit of interest in other people helps too. A small nuance that makes a significant difference in approach. And be mindful of what you talk about, what her tendencies are, her personality. The more information you build up, the more you have to work with. You can actually do these things naturally, but going through these processes builds confidence and helps you establish those skills.
Anyway, I hope you are able to get something out of this. As I promised, some links to conversation techniques, topics and questions.
Conversation techniques
Killer Conversation Starters | Science of People
http://iteslj.org/questions/
If you require anymore assistance you can contact me her anytime. Best of luck
