Chang'e is a really strong mage right now with a lot of potential. Her passive allows her to stack up damage whenever she lands an ability and this is why it's import to build attack speed for her third and fourth item. Every time you hit an opponent with her buffed auto attack (that she gets from her second ability) she deals more damage to her opponent with her next ability. This is why I go for a feather of heaven as my third and fourth item. It gives me the movement speed, damage, and attack speed that I'm looking for.
You can be super flexible with your fist item. If you're looking for damage I tend to go for a clock of destiny which gives me mana and damage that stacks throughout the game (until it hits 10 stacks), but going for an item that gives you mana regeneration or cool down reduction could also benefit Chang'e (Like Enchanted Talisman or Calamity reaper).
For her 2nd item I always go for either Magic Shoes or Rapid Boots (depending on what you build as your first item). If you decide to go for cool down reduction in your first item (Enchanted Talisman and Calamity Reaper) then I would personally go for Rapid Boots to get that extra movement speed to roam from lane to lane. If you go for a Clock of Destiny as your first item then I suggest you go for Magic Shoes which will give you the cool down reduction that you didn't take in your first item.
I always go for a Holy Crystal for my fourth item for massive damage
Your last item is determined based on how fed you are and who you're playing against. If you're playing against a high-damage team with lots of ability power then I would go for Athena's Shield:
If you're playing against a high-damage team with lots of attack damage (or any game with 2 marksman) I would go for Immortality:
If you're fed and dominating in the game then I would go for either of these three items (based on your preferences). Wind Talker can provide you with more movement speed and attack speed which is really good for mobility and melting enemies away with auto attacks. Necklace of Endurance is good because it provides cool down reduction, damage, and life steal. The passive on Necklace of Endurance is also useful against Estes and other supports that heal. Finally Ice Queen Wand is good because not only does it give you movement speed, damage, and magical life steal, but it also gives your auto attacks a slowing effect which is really good.
And that completes mt item guide for Chang'e!