How did Tecna gain her Enchantix?

She didn't save anyone for her home planet, but she saved like the whole Magic Universe, by closing that portal and by making sure no criminal ever gets out. I think that's actually the biggest sacrifice out of them all, because she would never be able to get out.

The portal was about to destroy the entire universe anyway, so when she closed it she made a huge sacrifice. Also, closing it saved everyone in the magical dimension, including everyone from her home planet. :)

The closing of the Omega Dimension portal is possibly the most under-appreciated act of any of the Winx characters. But this single purposeful decision by Tecna not only earned her the Enchantix transformation but it saved the entire Magic Universe - not only did it fit her character but it effectively "killed" her for 5 episodes. No, she did not save any single person - but through strength of will she saved all people. Much like Bloom willed herself to an imperfect Enchantix not long after as her home planet was barren.

It should be noted that even without the Enchantix transformation Tecna was able to breach the Omega Dimension portal - something that none of the other already empowered Winx could do.