She seems to prefer using daggers above other One-Handed weapons given to her, even if they have a higher damage rating (e.g. Dragonbone Dagger w/ 109 dmg. > Dragonbone War Axe w/ 194 dmg.), however that is not always the case.
While her dialogue as a spouse is identical to the others, Iona's delivery is rather stark, almost forced.
If one kills a chicken in the garden at Honeyside, she may attack upon entering Honeyside because she is appointed to protect the property. If she is a follower, she may leave the Dragonborn's service immediately and attack.
If Iona dies, a courier will soon appear and give a letter of inheritance and some gold (minus the Jarl's tax) to the Dragonborn.
Always add 360 , PS3 , or PC to clarify which system the bug appears on.
It is possible that upon completion of the full Meridia quest: The Break of Dawn with Iona, she will disappear. She does not return to Honeyside even after many days. As the Dragonborn cannot release a follower who is not present, she cannot be replaced with another follower and a reload is necessary.
PC(Fix) It is possible to use the console to move her back to the Dragonborn, first using "prid 000A2C93" then "moveto player" (confirmation needed).
PC 360 PS3 After the Dragonborn becomes a Thane of Riften, Iona may simply never appear. On the PC, this bug occurs when the Jarl's speech stops before she names Iona the Dragonborn's housecarl.
PC(Fix) Use the console command player.placeatme <BaseID> <#> to create an Iona in front of the Dragonborn. She will act as if spawned by the game as normal.
360 Within the Hearthfire DLC, if the Dragonborn appoints Iona as steward, she may disappear entirely from the game.