There could be many reasons why an apple tree does not produce fruit. If there is no fruit set after flowering, you may need a pollinator. The varieties that pollinate a Pink Lady are Royal Gala, Granny Smith and Red Delicious, try one of them. If it does set fruit feeding the tree with a complete fertiliser, mulching around the tree and keeping it well watered through summer. Should it set fruit, then drop it all, check the fruit for insect activity inside near core.