Tiana's ability will check for the card type at the time the ability that creates the delayed trigger is triggered. This means that the card will be returned to your hand even if it's not currently an aura or equipment while in your graveyard.
From Tiana's Gatherer rulings, emphasis mine:
Tiana’s last ability triggers and creates a delayed triggered ability that will let you return the Aura or Equipment during the next end step[...]
And, from CR603.7, which deals with delayed triggers, emphasis mine:
603.7c A delayed triggered ability that refers to a particular object still affects it even if the object changes characteristics[...]
And, to clarify what are characteristics, we refer to rule 109.3, emphasis mine:
An object’s characteristics are name, mana cost, color, color indicator, card type, subtype, supertype, rules text, [...]
Since the ability triggers when an aura or equipment leaves the battlefield (and is put into a graveyard), it looks back in time to the object that left the battlefield rather than the object in the graveyard.
This is governed by rule 603.10a:
603.10a Some zone-change triggers look back in time. These are leaves-the-battlefield abilities, abilities that trigger when a card leaves a graveyard, and abilities that trigger when an object that all players can see is put into a hand or library.