Does Lightning have an L'cie brand? Does it really located on her chest?
If Lightning isn't an L'cie, then how did she use magic?
If Lightning is an L'cie, then how about Hope?
That's all.
If you can't answer some of my questions, then don't answer it.

Yes, she becomes an l'cie like the rest of the party, and her brand is apparently located on her left breast (according to FF Wiki anyway).

All the party are from the beginning, or become eventually, l'cie during the course of the game, including Hope (his brand is on his left hand - it's partially covered by a glove)