Hi nellie,
Go out and enjoy yourself! it will be nice to have company. Run at your usual pace, see how things go. It won't do you any good to try and keep up with someone too much faster, but if she will stick to your pace to start with you may feel you can speed up in time.
Last summer when I hadn't been running long, I tried to keep up with my 'elder' sister....big mistake! it zapped my confidence. I meet up with my running partner once a week, she was 8 mins behind me on the five mile race, but we can still run together ok when we can. Perhaps suggest going at your pace but adding some extra distance?
Just see how it goes, but make sure you enjoy it!
Good luck, keep us posted.
Lyn.