"Harry saw Luna, all eyes in her white face..." What does this line from the Deathly Hallows mean?

Solution 1:

Taking a guess from the context of the chapter, the scoobies are in a dark escape-proof cellar prison, hearing Hermonie being tortured by Bellatrix. Luna and the others have been there for a while, and we have been told/implied that Luna has also been tortured. Dean had been bloodied. Add to that, the dark room was just lit up by tiny suns.

This leads to a possible meaning. That is all eyes in her white face could be related to the phrase all teeth and lips (meaning huge smile or grin) or wide-eyed (Wide Eyes and Shrunken Irises trope), meaning that her eyes were huge in comparison to normal, and her face was pale and drained of blood from fright (you know, more pale than normal). She is likely terrified of the situation, and of what she sees around her when the lights turn on.