Lump over eye

Maybe she has knocked against something and there is a foreign body in it - thorn maybe? Have you tried having a look at it to see if it is hard or soft - could it be a peck that has become infected? You won't really know unless you pick her up and have a good look at it. If it looks like an infected wound, bathe it and put a little antiseptic cream on it, but make sure that none of it can get into her eye and that there's not too much cream to attract pecks from the other birds.