The conditions for forming a stealth cleric are rare, both intrinsically and by compact. Gods cannot go about stealth-clericing whomsoever they please.
By compact, to make any cleric, they must have called out to You, or to a predicate that includes You not too broadly. The natures of god and mortal must be sufficiently aligned, as always for clerics; the only possible exception is your oracle, if you are foolish enough to have one of those, rather than zero.
For a stealth cleric to be permitted, by compact, it must be the case that if this clerichood could not be so concealed, the god would not trouble to bestow it at all.
And most improbably of all: The pressure of a god upon a mortal's soul, impressing clerichood into it, is usually very detectable to mortals even if you try to be slow and gentle about it. Even if it is not a revelation in glory, it's there, and the mortal might be suspicious of what had just occurred. Especially they'd just prayed to some god or any god for aid.
To create a stealth cleric, she must be extremely distracted while that is happening.
But these strange conditions are all met. And so, like trying to kiss a kitten's forehead softly enough not to wake it, Irori presses himself into Carissa Sevar but gently, not opening yet the new channels whose outlines are traced into her, only marking her as His.