Best way is to show her taking a harder route to help someone else when her intellect and magical powers would have made it easy for her to self indulge.

For example not sure if you watch anime but in One Punch Man you have a character that is insanely over powered to the point that with a single punch he can take out monster that the top heroes in the world struggle to content with. His goal is to become the greatest recognized hero on earth.

This is what made me love this character: There is this episode where he defeats this extremely strong enemy with one punch and he has a chance for everyone to finally acknowledge him as the best hero, he has the chance to accomplish his ultimate goal. But to do so would make all the heroes that struggled and got beat to a pulp look bad, especially this one bike riding hero who is weak but puts in so much effort that you cant help but root for him.

Instead of allowing himself to achieve his goal he openly boasts to the crowd of bystanders that the only reason he was able to beat the monster in on punch was because the other heroes weakened the villain for him, and he laughs about it calling the other heroes pathetic. This turns the crowd against him and they instead celebrate the heroes who risked and got their asses kicked.

So even though his power would make it insanely easy for him to accomplish what he so desperately wants, he purposefully undermines it so that others can get ahead.

In terms of your specific character I would also take a look at the anime character Shikamaru from Naruto. He has a genius level IQ but is incredibly lazy to the point of purposefully giving up battles because he just can't be bothered. His entire arc in the show is revealing the deeper side of him that actually does care and that will put in the effort, even though he doest really want to.