There could be various reasons. Maybe the story didn't require Randy's presence to progress the narrative, or they wanted to shake up the dynamics and introduce new characters instead. It's all part of the creative process behind the movie.
It could be for a variety of reasons. Maybe the story needed a new dynamic or there were scheduling conflicts. Sometimes creative decisions are made to give the story a fresh twist.
It could be that the script or the director's vision didn't call for her character this time around. Or perhaps she simply wasn't interested in reprising the role.