Tellu made her first appearance in episode 121 of Sailormoon Super (Or as you may know it, SMS) 121 was the episode in which Tellu really took action, but she actually appeared briefly in 120.

Episode 120
Mimete, the second of the Witches 5, had programmed her body into a computer so she wouldn't die. Tellu showed up and argued with a screaming Mimete. Finally, she pulled the plug and Mimete died.

Episode 121
We first see Tellu in this episode when she is typing at her computer. The phone rings and she answers. It's Professor Tomoe, Hotaru's mad scientist father. He expressed his interest in her plan to obtain heart crystals (to awaken Mistress Nine who will bring the ruin) by using plants which, in essence, suck the life out of people and release a heart crystal. She tells the professor that she is ready and she turns on the lights. The room shows zillions of plants.We next see Tellu in her plant shop. She is explaining that her plants don't need fertilizer or water and are inexpensive.Setsuna buys one to study it. It attacks her, but her talisman protects her.Later, Tellu gives a plant to Chibi-usa, explaining that it brings good luck. She decides to give it to Hotaru. Eventually, Chibi-usa, Usagi and Setsuna decide to check out the flower shop. They arrive just in time to see Tellu take the heart crystals of several customers and collect the crystals in a black star in her hand.They transform and appear before Tellu.

Tellu shoots plant vines at Chibimoon, but she uses her Pink Sugar Heart Attack (and it actually works!) but Tellu retaliates and shoos more vines at Chibimoon. Pluto throws herself in front of Chibimoon just in time and is, I guess, electrocuted. Tuxedo Kamen saves Pluto, and Sailormoon transforms into Supersailormoon to kill all the plants. This really annoys Tellu. She takes out a flower pot and a huge plant comes out of it. She explains that it attacks those with pure heart crystals, then destroys itself to kill the person as well and obtain their heart crystal. She is about to leave with her black star, but Tuxedo Kamen destroys it with a rose. Tellu is left among the heart crystals and the plant goes after her. The last we see is Tellu wrapping the plant with her vines and trying to electrocute it.We hear a bloodcurdling scream, and then, sadly, Tellu dies.