Janet Fielding was able to prove herself as a wonderful actress especially in Kinda and Snakedance. Kinda is rather a Tegan focused story, and she is seen slowly going into a state of madness due to an evil being called the Mara. The Doctor believes he was able to destroy the Mara in Kinda, but he is proven wrong in the sequel Snakedance. Snakedance is when Tegan really shines. She has just come back to the TARDIS, after being left behind at the end of Time-flight. She is picked up again by the Doctor and Nyssa at the end of Arc of Infinity. It is the sequel to Kinda, and we see the return of the Mara. I think in Snakedance, Tegan's mentality seems a bit more fragile ever since dealing with the Mara the first time. At this point the Doctor is still reluctant to get along with Tegan, yet he welcomes her back on to the TARDIS. Perhaps because he feels he needs that driving edge that she's got to keep him going, but he still wonders if she'll be the same as she was the first time around. It's at the end of Snakedance we see a friendship building between Tegan and the Doctor that we never imagined seeing in the previous season. We see a very distraught Tegan, and the Doctor approaches and sits with her, and wraps his arm around her, comforting her. It's a very sweet and emotional scene. Season Twenty saw Tegan calming down a bit. She didn't trust Turlough however, and with very good reason. Turlough came across deceptive, cowardly, and a sneak. Tegan had good instincts that there was something strange going on with Turlough, but she and Nyssa couldn't figure that out. She became brutally protective of the Doctor. It may have come across complaining, but to be honest, the Doctor has always had a flaw in trying to trust every single person that comes into his TARDIS. He would not listen to Tegan and even Nyssa to some extent when they felt Turlough was bad news.