Ioreth is the oldest of the women serving in the Houses of Healing. As she looks at Faramir, lying there with a fever that won't die down, Ioreth comments in passing, "Would that there were kings in Gondor, as there were once upon a time, they say! For it is said in the old lore: The hands of the king are the hands of a healer." (5.8.24).
Hey, now there's an idea. Gandalf wonders if Ioreth has heard the news that a king has come back to Gondor. Ioreth replies grouchily: "I have been too busy with this and that to heed all the crying and shouting [...] All I hope is that those murdering devils do not come to this House and trouble the sick" (5.8.26). So Ioreth is not only the possessor of precisely the old lore that Gandalf needs to heal Éowyn, Merry, and Faramir, but she is also a dedicated nurse, which is essential in these hard times.
Gandalf calls Ioreth a "wise-woman of Gondor" (5.8.43), and indeed, without her observation about kingly hands and healing, Merry, Éowyn, and Faramir all might have died.
On the other hand, sure, Ioreth is helpful, but she is also mostly a comic character. Her focus on healing the sick, which prevents her from hearing news of the arrival of the king, shows that she is relatively narrow-minded (in both good and bad ways).
When Aragorn arrives and asks for athelas, she gives him a whole long spiel: "Oh that! [...] Well, if your lordship had named it at first I could have told you [...] indeed I have often said to my sisters when we came upon it growing in the woods: 'kingsfoil,' I said, ''tis a strange name, and I wonder why 'tis called so; for if I were a king, I would have plants more bright in my garden'" (5.8.58) and so on. She blathers on and on without really thinking about what she is saying (or to whom she's saying it), nor does she worry about wasting anyone's time. Aragorn finally tells her to "run as quick as [her] tongue" (5.8.59) to get athelas if there is any in the City. In other words, get a move on, lady, if you want to keep your job.
So Ioreth comes off as a bit foolish, something like the classic comedic nurse characters you often get in Shakespeare plays (think of the nurse in Romeo and Juliet,for example). At least, as comic relief, she lightens up the overall sense of gloom that hangs over the Gondor chapters before the Ring gets destroyed.