What klunick
said. Just hold the wet washcloth or paper towel on her nose long enough to soften the food before you start wiping, if she'll hold still long enough.
There are baby washcloths that might be a bit softer than regular washcloths, maybe even a moistened cotton ball. Also, if at all possible check her nose immediately after she eats, when the food has not had a chance to dry any - that should make it easier to remove and avoid you having to hold something over her nose waiting for it to soften.