Resource: Exhaust Black Widow’s Gauntlet → generate a [Wild] resource for a Preparation card.

My son and I were playing yesterday. He was Aggression Black Widow and I was Protection Captain America. I had 2 cost Protection card Defensive Stance in hand and came up a resource short. He offered to use Widow’s Gauntlet to pay for my deficiency. I told him unfortunately that it didn't work that way... but I did want to make sure what everyone else thought. The wording does seem some what different than other cards like this (Enhanced X, Quincarrier, etc).

I believe you played this correctly. Under "Cost" page 5 of the RR "While a player is paying a cost, that player must pay costs with cards and/or game elements they control".

I think another key to this answer is the Resource keyword, regardless of the text that follows it. It automatically implies that it cannot be used for another player, as generating resources can only be done for cards you play yourself.