According to Wikipedia, her episodes were from the 3rd season:

C9 "Sarcophagus" Fiona Cumming Tanith Lee 3 March 1980 9.9 (22) The Liberator comes across a derelict alien ship and Avon, Vila and Cally teleport over to investigate. They find the ship has only one deck and contains a corpse and a strange artefact. After Cally accidentally triggers a self-destruct, all three hurry back to the Liberator and bring the artefact with them. The device then unleashes a ghostly presence that stalks the ship. It takes over Cally's mind sending her into unconsciousness, then shutsdown both Zen and Orac and drains the ship's power systems. All the while the rest of the crew experience strange poltergeist-like happenings and finally confront the spirit, who assumes Cally's likeness. They then look for a means to destroy the entity before it enslaves them all. Guest Star: Jan Chappell (as The Alien)

and from the 4th season:

D9 "Sand" Vivienne Cozens Tanith Lee 23 November 1981 8.3 (87) Servalan arrives at the planet Virn – a world covered in strange green sand – to find out what happened to a group of Federation researchers who had gone missing five years ago soon after uncovering a substance with unique energy potential. The Scorpio crew follow her to the planet, curious to find out what she is up to. When Servalan arrives, her ship is disabled and her associate, Investigator Reeve, turns against her. She finds herself alone until encountering Tarrant who teleported down with Dayna to track her. The two must work together to survive and find shelter in a bunker against the green sand, which seems to be a living, intelligent lifeform. Meanwhile, a strange energy storm cripples Scorpio preventing it from performing a rescue. Guest Stars: Stephen Yardley (as Reeve), Daniel Hill (as Chasgo), Jonathan David (as Keller), Peter Craze (as Servalan's assistant), Michael Gaunt (as Computer)

I vaguely recall "Sand" and the title of "Sarcophagus" is familiar, but I don't recall them otherwise.

I think "Sarcophagus" is the one I was thinking of.

Sand is the superhot sexy one that has all the virtues of good fanfic. It's where Servalan boinks one of the heroes.

Seveneves: the first half is Neal Stephenson in what I consider his best form. Narratively compelling but with plenty of willingness to go theoretical and descriptive for pages on end when appropriate. Near future. Very cool hard science for anybody interested even slightly in space exploration.

The second half jumps 5000 years and felt like an Arthur C Clarke novel but he is not nearly as good at far future out there weirdness as Clarke. It was perfectly decent but wasn't wonderful. There were several moments where I thought his extrapolations were ridiculous and far too reliant on coincidence.

Gris, I'm working through Seveneves right now.

After reading Uprooted in 12 hours. And I'll do it again.

I love Stephenson (and I checked to see if this one has an ending) but this is a slow read for some reason.

Definitely. I paid 3 dollars for the audio upgrade with my kindle copy (which is BRILLIANT) and it was a good choice for that. The technical passages ended up feeling like an interesting podcast rather than a manual.

All right, you all were right about Station Eleven. What a marvelous book.

Wasn't it? I really loved it.

Speaking of good stuff, I really liked your story, P-C. Fun stuff!

I haven't read your story yet, Sunil. But I did buy the Kindle version.