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.), but 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 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.
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 one cannot release a follower who is not present, she cannot be replaced with another follower and a reload is necessary. On the PC, it is possible to use the console to move her back to the player, first using "prid 000A2C93" then "moveto player" (confirmation needed).
360 PC PS3 After the player becomes a Thane of Riften, Iona may simply never appear. On the PC, this bug occurs because the Jarl's speech stops before she names Iona the Player's housecarl.
360 Iona can accept items to carry but will sometimes not equip wearable armor even when base protection is scaled beyond her standard items (i.e. Dragonbone Armor or Daedric Armor) with Hearthfire DLC.