They
did only have her on screen for one job and not one second more. That scene happens near the end of the movie, it's less than 10 seconds and nothing more than a brief cameo, which that movie had plenty of.
Scene for scene, Cushing was done a lot better, and I do agree that they should have spent some more time on Fisher. However,
if ILM is to be believed, Fisher liked it. Can't exactly ask her directly now, can we?