be sure to communicate well with your friend about your plans as the rabbit. is this a big race, or will it mostly be your friend going for a fast time alone? will you need to run the 1st 100 around 13 seconds to get into the lead, or can you go out in 14.5 and ease into the lead?
in the race itself, you want to do your very best to hit the 200 around 0.5-1.0 seconds ahead of your friend's goal pace. much faster or slower than that can really screw things up. if you do that and you are exhausted, just push really hard through 300 and ease off the track (to the inside!!!) on the homestretch. make sure your friend knows that you will be exiting the track to the inside so she doesn't run on your inside.
as for the workout, i'd focus on running multiple 200s in your goal pace. you want to be as locked into that feeling as possible.