She was the microwave used in the first half of Season 3 (the other half had Helga).
Experiments: 45 - 62
Brand: Sharp Carousel
Followed By: Helga
Sandra was killed by Diane. In the special Microwave a Microwave, they microwaved Diane's parts inside of Sandra. Sandra eventually gave up after 30 seconds and Diane killed Sandra.
The guys threw her out and had Helga for the next half.