Gladys is Ned Tedford's pet plant and sole companion. "She" is a geranium in a plant pot, whom Ned often talks to during his lonely jobs. Gladys is most closely related to an Americana Pink Zonal Geranium.
Being nothing but a flower, Gladys obviously doesn't talk back, but Ned often talks as if she has her own opinions and responses.
History
First appearing with her owner in Slingshot, Gladys accompanied Ned Tedford on asteroid 21 Lutetia, where he worked otherwise alone on the Golvanna Mine. When a solar flare struck the asteroid and caused the mining drill to slip into the core, it resulted in an eruption that pushed the asteroid onto a collision course with the sun. Gladys and Ned were saved by Alan and Kayo in Thunderbird 3.
Gladys then appears in Under Pressure. In this episode, Ned works on a heavy metal extraction platform carrying toxic waste. When an on board fire disables the vehicle's ability to steer, Thunderbird 4 is required to evacuate them. Gordon Tracy, rightfully, thought Ned was insane for talking to Gladys. Along the bumpy ride in the extraction platform, Gladys would shake slightly, giving the impression of nodding or shaking her head to the ramblings of Ned Tedford.
It appears in Undercover and Up from the Depths Part 2 as well with Ned.