User blog comment:Edrea/Is Morgana more powerful than Merlin?/@comment-10341849-20130628150948/@comment-5102537-20130629103819

"If Morgana became immortal or powerful because Aithusa, then Merlin should be more poweful tenfold, how many times did he receieved healing from Kilgharrah, I believe many more than Morgana?

''And Kilgharrah even gave his power to Merlin to heal Morgana, right? (Yea, I just remembered, if that was the case, then after that Merlin should have not failed any more spell like he did numerous times)."''

You're right. My guess is that the Triple Goddess somehow gave the power to her since Morgana was the last High Priestess, therefore needed more power because there weren't any other priests or priestesses anymore. If this was the case, the Triple Goddess obviously didn't bet on Merlin and probably knew that he wouldn't want her opressing dogmas being worshipped and restored.

Just my speculation. I think we will never know and I don't know why this wasn't explained.