I'm a bit curious about Frieren's intentions as well, especially assuming she cares more about improving people's means of resisting demon's assaults than a certification she knows is not necessary for her to have, since she is confident Fern will obtain it.
It may also be critically important to note that many, if not most of the other mages are willing to kill, or approve of killing in order to obtain ranking. In this way, their morality and behavior resemble the demons', Frieren's only real enemies.
Though "Soul Track" and it's counteracting shield spell may have improved through public study, as what Frieren called a development in magic, we know that most other magic has been lost, and mages have become less common.
I believe that, like Kraft the monk, she has an interest as a surviving elf to the preservation of human (and equivalent) life, and to peace, both in the immediate and the long term. Not only is she preventing mages from murdering each other at the moment, she is showcasing an effective solution to the whole of mage society, beyond what is now only violent, martial magic.
At least, that is my hope.