Young (The Sea Devil)

Miss Young was a companion of the Third and Fourth Doctors for a brief time during their early years on Earth.

Biography
Miss Young worked for the BBC in a secretarial role. She invited the Third Doctor to a party being thrown by her employers, which he attended after investigating a missing film crew. (PROSE: Countdown to TV Action)

On one occasion, she went to Scotland with the Fourth Doctor, in Bessie to meet with Professor McBane, an old friend of the Doctor who had summoned him. The friend revealed that a meteor had crash landed in oil rig waters, and he wanted the Doctor's input on the chance of alien hostility. As the group flew over the area in a helicopter, giant tentacles arose from the sea and began attacking a local ship. The Doctor was able to take a sample of the pink substance from the creature back to the laboratory, where he discovered that it was seaweed contaminated from radiation from deep space brought by the meteorite. Furthermore, the mutated seaweed was attracted to sound, so the sound of the oil rig put it in danger.

The Doctor and Miss Young headed out on a boat, using a sound-emitting gadget to attract the mutated seaweed. A tentacle grabbed the Doctor, but Miss Young cut it off. They lured the mutation into a shallow bay where it couldn't dive and dropped drums of petrol from the boat. After they were flown out of the area, the petrol was lite on fire, killing the beast. Afterwards, the Doctor and Miss Young drove back to the TARDIS for more adventures. (COMIC: The Sea Devil)

Miss Young's time as a companion was documented in the Death's Head Interactive Archive. (COMIC: The Incomplete Death's Head)

Behind the scenes
Never identified by a first name, Miss Young was a comic-exclusive "filler companion" created by TV Comic, apparently as a replacement for Leela, who had previously been featured in 1977 TV Comic stories. TV Comic Annual 1979 was published in September 1978, by which time Louise Jameson had left the series, but it is also worth nothing that most of the TV Comic stories from 1978 feature the Doctor travelling alone.

This implies Miss Young was either created due to lack of information about the future of the show, or because TV Comic did not want to pay extra licensing fees for the use of the Doctor's new television companion Romana, as played by Mary Tamm — which is similar with why the original TV Comic companion characters of John and Gillian were created.