I am afraid to go running with a partner... HELP!?

I was out one day doing the Couch to 5k running program, and I was doing my first running interval (I was going pretty fast) when this athletic girl that lives by me that I go to school with drove past me and saw me. Now she wanted to know if she could go running with me(!). I am NOT a fast runner (my fasted run was like a 9:15 and I am 14 years old!), and if I go fast, I can't maintain it. I want to do it, but I am scared I won't be able to keep up. To top that all off, we live in a hilly area, so it makes it even more difficult! Please, I could use some advise. Thanks :)