What I love about Misaka is that even though on the outside, people call her righteous and heroic, she knows herself she isn't. She's a bit selfish in a way that she's willing to hurt people if it's for her friends and wouldn't hesitate to. Though if possible, she would like to avoid conflict in general and probably wouldn't want to kill. In some ways, she actually admires Touma that he's able to accomplish such feats of saving his enemy and everyone more than her, since if possible, she would like to achieve it as well but knows her power isn't enough to. Which is kind of the reason why she can't call herself a hero because she herself is aware that she doesn't have the power to save everyone, so it's a bit of a reason why she prioritizes her friends first. You can already tell that she thinks Touma as a greater being than her and would like to catch up to him if possible just from that sentence she says.
Truthfully, I wish this characteristic of her admiring Touma's aspects such as his resolve is shown more in Index since really the only thing going (anime-wise) is the romantic and tsundere aspect :/ Index doesn't do her enough justice to see how amazing of a character Misaka Mikoto is, though I can't blame it since Touma's perspective sadly cannot see all of Misaka's traits...
SPOILERS FROM HERE ON OUT!!! YOU'VE BEEN WARNED!!!!
Though I believe in the light novels (NT), you do see that side of hers later on, where she knew that no matter how hard she tried, she could never stand on the same stage as him and she felt truly inferior. Though because of that, she becomes more power hungry (something that a lot of LVL 5's go through it seems...) and searches for ways to exponentially power up, with any cost, if it means to help Touma. Truly the LN does treat her better from there on out and I actually hope a bit Railgun does put light upon this, where Misaka does go to the dark zone and willing to be evil if it's for those important to her (like Misaka Imouto~~~~)
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