So you did put a lot of thoughts in to it. Great!
Fall in love: to begin to feel romantic love for someone
People fall in love and stay in love. You mama fell in love with you father long time ago, and she is still in love with him till today. How nice! :)
blush: show shyness, embarrassment, or shame by becoming red in the face.
Flush: (of a person's skin, face, etc.) become red and hot, typically as the result of illness or strong emotion.
So these two words both have the meaning that someone's face becomes red, but resulting from different emotions. It depends on what you try to express. I thought you meant she was kind of embarrassed. :)