Daisy has changed a lot over time, but its original pronunciation was by far the best. In literature, daisy has been corrupted a tremendous amount. In Modern English, it also used to be spelled daisie and daysie. Going backwards, the latter is perhaps more appropriate, because in Middle English, daisy was spelled several ways, including daysie, daieseyghe, and dayseye. The reason this changed so much over time is because nobody could agree on the proper spelling. However, when traced further back to Old English, the spelling was uniform (daeges eage), mainly because there weren't many people writing back then. You may have noticed a pattern to the pronunciations by now: they all sound like day's eye. In fact, that is what it used to be! Daisy, though it's hard to guess now, is a combination of the Old English words daeges, "day's", and eage, "eye". It was named thus because the petals open at dawn and close at dusk (similarly, in Latin it was solis oculus, or "sun's eye"; this likely had an influence on daeges eage). Daisy as a woman's name was apparently a nickname for Margaret (and today is as appropriate as Peggy).
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.