How to propose this girl?

I want to propose a girl who was my student. She is 21 and i m now 26. Actually, I was a lecturer in a college and she was my student. i left the college 1 year ago and joined in a new company. I liked her from very earlier days but could not express. Sometimes we talk in phone but very formal mainly about her studies. but I liked her very much and want to propose. And one thing I have not seen her for a year. i don't know whether she will accept or not.She is extremely intelligent. very much carrier concern .... and She has very strong personality...I am very much attracted by her intelligence and personality.. I don't want to lose her. Pls help.