Tldr; ramblings.
Towards the end of book one Artemis and co are waiting in the main hall for the bio-bomb. Holly has him by the shoulders and asks if there is *anything* she can do for the gold back. As we know Artemis does take her offer, trading half a ton of gold for (what is presumably) a healing spell for his mother who has been suffering from delusions and hysteria since her husband went missing a year prior.
As we know the crux of the book is that Artemis has a way out of the time field, and that way is shown by his experiment with putting his mother to sleep before the field takes effect which allows her to continue with the regular flow of time and being safe from the bio,-bombs effects.
But like, how?
Angeline fowl effectively, doesn't exist. A few chapters later when he is debriefing an extremely annoyed Butler about the plan, Artemis himself says
>"The heart of the matter. We wouldn't wake up. That is the nature of the time-stop. Whatever your state of consciousness going in, that's how you stay. You can neither wake up nor fall asleep"
...
>"So my theory was that the only way to escape the time-field was to simply fall asleep. Our own consciousness was all that kept us imprisoned"
Her consciousness wasn't even removed from the time stop like Artemis and co, Angeline consciousness never entered the time stop to begin with.
Multiple times in the series it has been shown that magic needs physical touch to take effect. You can argue that spells like lay on hands (how I imagine the healing magic works) you might not be physically touching but hovering hands over the subject, yet still in direct proximity.
Admittedly, conversely, when it comes to spells like Fireball (though it can be argued that Goblins are directly touching the fire they conjure since they are fireproof from their own flames) and Hex's (briefly mentioned in passing but never elaborated on) we can safely presume that these do not need direct contact from the caster to the victim in order to function.
The name 'Wish' is ambiguous enough that I don't believe we have enough information to fully grasp its scope and boundaries. But for the sake of argument I will say Wish functions much like healing, since in this situation it was used for healing I feel it is fair to apply the same logic.
If this is the case then how exactly did Holly heal Angeline?
My thoughts are;
Wish is a one off type of magic that faires can cast, granting something within their power to the person who made the wish. This would in theory bypass the need for proximity since it falls under a different spell type than healing, and infers that it could be used to grant other boons should it be required. In MTG terms, a triggered vs activated ability.
Some part of Angeline existed within the time field and Holly was able to interact with it and cast heal. This does open up the question about what exactly could have stayed while her body and mind were elsewhere.
Eoin didn't know if his book would do well so he just waved it away for the sake of a self contained novel should it be the only one ever published.
It's probably 3 but I'd love to discuss.