skirting the line of Mary Sue Super heroine

[Akisa]

So I want to make a story where super hero powers comes to the world just prior to ww2. Comic books exist in this world but has no involvement. The powers in the story commissioned the super hero for WW2 (there is a wide range of powers level with the strongest is very similar to movie Ironman).

So I want to make a super heroine that skirts the line of Mary Sue. So I'm wondering anyone have tips of making a Mary Sue likeable (such Superman or Goku)?

[Rift_Wolf]

Character flaws that are actually flaws. Not a scar that makes her cooler. Mary Sue refers to a character who is immediately good at whatever he or she does and overshadows other characters. People more familiar with Superman and Goku might correct me, but they have flaws in social interaction and life problems to offset their strength in a standup fight.
Adding superheroes to WWII... From what I gather about the captain America films, they wanted to separate fiction from history by having him fight HYDRA rather than nazis. Adding superheroes on the side of good might be seen as pro-war. Fiction seems to have no problems making supervillains/aliens/Vampires on the nazi side, though. This is because giving the villains an advantage makes them more credible as a threat.

[Lethologica]

Superpowers don't make a Mary Sue. Avoiding Suedom for a superhero is much the same as for any other character.

-Give other characters agency. Make your world larger than the MC and her decisions/actions/powers.
-Don't make everyone who likes/agrees with your MC good/reasonable or everyone who dislikes/disagrees with your MC bad/unreasonable. (Also, don't make everyone like/agree with your MC.)
-Allow your MC to be wrong/ignorant/naive...then call them on it, so they can learn and grow.
-Allow your MC to make wrong choices/to struggle/to fail. Force them to learn and grow.
-Present your MC with choices between two goods or two evils, not just choices between good and evil. You can probably get away with Taking A Third Option...once.