Many says that it's hard to get the four-leaf clover in the game and once you didn't get it the first time, it wouldn't be possible to see it again.
But I have something to say. If you were playing this game on your PC, it's not that hard to do.
When Lina asked you to find the clover, save the game Pressing Shift + F1 or F2 or F3, then look for it. If Ein didn't find it, load the Game by just pressing F1 or the one that you pressed with Shift and thei game will be back to where you saved it.