It was the Easter weekend, dude. She could have had a lot of family stuff going on. It takes only a second to "like" a pix, but it takes a little time to respond to a message. Wait a couple of days and try again. If you don't get a reply then, drop it and wait for her to contact you. If you go to school with her and you see her, smile and nod and say HI and go on with your day.