How to be able to take fashion shots at NIGHT?

I'm currently assigned by the school fashion show to take a fashion shot of one of the models at this location:

currently i'm in possession of a Canon Rebel t1i along with a 18-55mm f/3.5 and i'm goign to be given an external flash

i'm also in possession of a nikon d90, along with an 18-55mm lens [from a friend] adn an 85mm lens
and i'm able ot use teh school tripod

my question is how can i get a good 'fashion style' shot with the equipment i have been given.

and please don't ask why i have all of this stuff with me

Added (1). I'm kind of in a rush cause this assignment was not originally mine it was given to me because the photographer was unavailable so this came all of a sudden to me

I don't know, use a reflector

Try using reflecting umbrellas and maybe use a softbox if the flash is to bright.

No matter what you do, you will need a fast lens and the only one you have is the 85 mm

You can use a flash, but set your flash sync to rear shutter and shoot at a slow enough shutter speed to catch some of the ambient lighting.

You will really have to do some testing to assure great shots.

Set your ISO to 200 and the white balance to flash and go for it.