In Game Edit
Izerna is the first healer you get in the game and will function well as such. She will get a good amount of healing off and is relatively easy to promote. However she will be outclassed by a few of the later healers in the game. This is due to her low movement and slightly weaker personal tome.
Use her at first and if you feel you need 3 healers at endgame, but otherwise drop her in favor of better healers.