Jeyne Poole
0 Cost
0 STR
INT ICON
Ally.

Response: Discard Jeyne Poole from play to cancel the triggered effect of a card that just came out of Shadows.

Can this be used on Meera Reed, Guardian Wolf, or any of the "bring this card out of shadows and into play .... by paying the rest of it's gold cost" and similar wording. The problem is, they are not out of the shadows during the Step 1 - Initiation step, but only after the Step 2 - Save/Cancel responses step. So, there is no opportunity to cancel them. I just want to be sure that is the correct interpretation and that she is indeed a highly conditional piece of claim fodder.

Could be more useful with "cancel the triggered effect of a card with the Shadows crest".

You are correct. When cards like Meera, Guardian Wolf, Jaqen, etc. use their effects to come out of Shadows, they are not actually out of Shadows during the opportunity to cancel the effect. So Jeyne's "just came out of Shadows" restriction is not met.

She's really only effective against "after THIS card comes out of Shadows" Responses. That does cover a lot, though.