...Attacker dealt damage to Andira (in order to defeat her), which might trigger her ability before she is removed.
If it is a timing conflict, the active player gets to decide which happens first. Usually if Andira is being defeated, this is the Overlord's turn, but some Overlord cards might allow Andira to be attacked during a hero player's turn.
Exactly. "Andira suffers damage from an attack" is the trigger. This trigger has two notable effects in the case that the damage Andira has suffered equals her health:
1) She is defeated
2) the attacking figure suffers a damage.
Active player would determine which of these happens first. (Usually going to be OL).