Okay, Well mate, it depends which she buys.. There can be a complete spoiler bought (The MG Zr, all complete) or (the half circle cna be bought, which i think needs to be bonded on, via tigerseal (not too sure)) Now.. Simply open the boot, remove the trims so you expose exactly the spot under the standard spoiler, it should have i think two or three bolts attched to it (2 either side, 1 middle) Remove them.. then take the spoiler off the top, It will have a wire attached, its for the break light. Remove this (make sure you attached it again to the new spoiler) and Fitting is reversal of removal!
Now if you do buy the half circle, as said, im sure its a matter of tiger sealing it onto the standard spoiler (but wait for some one else to verify this )