LTsk8er2go-----The sooner you break it off, the less pain for her. The way to do it is, meet her face-to-face, look her square in the eye, and say "It's over". No other explanation needed.

Two possible reactions. She will either dissolve into a flood of tears, or she will punch you.

However, the desired result is that you are sending a clear message across to her. Years from now, she will thank you for having not wasted her time any further.

Good Luck.