It can be argued that she is a villain because she combined the Aurameres, creating an Altermere, which is made of pure energy and stole four of the five Guardians' powers:
The blob-like entity eventually found its way to Cornelia; after jumping out of Irma's window, it infused itself into The Guardian of Earth, giving her all five powers (which awoke Nerissa, who took great advantage of Luba's catastrophic mistake). Cornelia felt exceptionally powerful. So powerful in fact, she tried to bring Caleb, who was currently a flower, back to life.
Well, Luba didn't like that at all and paid Cornelia a visit, threatening to take Cornelia's power of Earth away forever if she did not surrender flower-Caleb to her. Cornelia was infuriated and bound Luba in vines, which Luba disintigrated with her staff and managed to transport Cornelia, the Caleb-flower, and herself to Kandrakar, then leaving the Guardian in a room to decide her fate. Cornelia still had her immense power and transformed Caleb back into a standard Murmurer, except he was seemingly mindless, not changing expression or moving at all. Cornelia cried over his motionless body, a tear landing on him, which gave him the strength to turn back into his humanoid Meridianite form.
Caleb and Cornelia stood trial, where the other Guardians regained their powers, Cornelia returning to have her Earth power (as all five of the Guardians' powers would have been too much for her to handle, and would have killed her), and Caleb stated that he was not a Murmerer of Phobos and swore to be a loyal servant of Kandrakar. Luba was enraged, saying she would not allow Caleb to join Candracar, and lunged (at either Cornelia or Caleb, perhaps, both), Caleb forced her back, knocking Luba to the ground, where she stated to the Oracle that this was the end of Kandrakar - and she wasn't going to stick around to save it. She then vanished on the spot, giving Caleb his first assignment to find her and bring her back unharmed.
Please remember that Luba did all this to protect the Oracle and Kandrakar, and the Oracle still says Luba is his "Dear old friend."
Luba was eventually found and is put on trial many times in Part II. She eventually and surprisingly sacrifices her life for the Guardians, and in doing so, she redeems herself. She is the one who brought Orube to Kandrakar and trained her to be Taranee's replacement as a W.I.T.C.H. girl. As you can see above, Luba played a significant role the Guardians' lives.
Chronology in the Animated series
In the cartoon, Luba plays a significantly smaller role. She's a feline-like member of the Council of Kandrakar and the Keeper of the Aurameres. She was forced to guard Kandrakar alone after Nerissa trapped the other Council members inside a bubble-like mini-Veil part way through season 2.
She did not mutiny or unknowingly create the Altermere and set Nerissa free. Luba helped the guardians in U is for Undivided telling them that Lillian she was the Heart of Earth. She also looks much younger. In the animated series Nerissa says that her old friend the Mage let her out. It also doesn't tell you how the altermeres were created.
|Arc 2: Nerissa's Revenge|
|Heroes:||W.I.T.C.H. (Guardians) · The Oracle · Yan Lin Matt Olsen · Caleb · Elyon Brown · C.H.Y.K.N.|
|Villains:||Nerissa · Shagon, the Hate · Khor, the Destroyer · Tridart, the Despair · Ember, the Pain|
|Items:||Heart of Kandrakar · Aurameres|
|Planets:||Earth · Kandrakar · Meridian|
|Issues:||013 · 014 · 015 · 016 · 017 · 018 · 019 · 020 · 021 · 022 · 023 · 024|
|Heroes:|| W.I.T.C.H. (Guardians)· Yan Lin · The Oracle · Caleb · Blunk · Luba · Elyon Brown · Vathek · Aldarn · Drake · Tynar · Alborn · Miriadel · Ironwood · Bitterroot · Lillian Hale |
Regents of Earth : Matt Olsen · Mr. Huggles · Napoleon
|Villains:|| Nerissa · Prince Phobos · Cedric · Jeek |
Knights of Vengeance : Raythor · Tracker · Sandpit · Gargoyle · Frost · Miranda
Knights of Destruction : Shagon · Khor · Tridart · Ember
C.H.Y.K.N. : Cassidy · Halinor · Kadma
|Items:||Heart of Kandrakar · Aurameres · Heart of Zamballa · Seal of Nerissa · Horn of Hypnos · Tooth of Tonga · Mage Ring · The Great Ring|
|Planets:||Earth · Meridian · Kandrakar · Zamballa · Aridia|
|Episodes:||01 · 02 · 03 · 04 · 05 · 06 · 07 · 08 · 09 · 10 · 11 · 12 · 13 · 14 · 15 · 16 · 17 · 18 · 19 · 20 · 21 · 22 · 23 · 24 · 25 · 26|