Counsellor Grerbe is the "First among Equals" on a spaceship orbiting Earth (well, L4) and studying Humans. That is, since this is a science expedition, she is the de-facto leader unless an emergency arises.
She OKs most of the decisions the crew of the ship is afraid to make themselves. Big picture stuff. She was the one that authorized Alice Jenkins' abduction - but was not there when she woke up.
She stands, in her adopted bipedal form, about 203 centimeters. That is, literally looking down on everyone.
Counsellor Grerbe appears for a bit in It's Like Kissing a Test Tube