Enter her layer.
When you are in the Black Widow's secret headquarters, and go past the guards, there is a door with a lock requiring the Black Widow card. Press USE on the card and it opens the door to where you fight the Black Widow.
When you find the scream you will be near the black widow's lair then you use it
When the Black Widow catches you , you will have to pass the guard and at top you will use your card
You use it late in the game to reach the Black Widow in her trove of stolen art. Its use will be immediately obvious from the card-reader on a door you encounter.
Use the key card to open the treasure room and battle the Black Widow. (see related questions)
You only use the Black Widow key card at the end of the island, to open the sliding doors in her secret hiding place.
You do not use it when you find it. When you get free in the Black Widow's hideout, the key card will open the door to her collection of stolen treasures, where you battle her at the end of the game.
get your key and open the house that is locked and go inside
Once you get the card you see the black widow on it and go to that house and go inside with the key and you will find the the painting and click on it then once you find the door use the card.
The key card does not open any house. You use it much later to enter the underground treasure trove of the black widow.
It is the last part of the island, when you have discovered the stolen painting and get kidnapped by the Black Widow. Get past her guards and use the key card to begin the final battle.
When you are in the Black Widow's secret headquarters, and go past the guards, there is a door with a lock requiring the Black Widow card. Press USE on the card and it opens the door to where you fight the Black Widow.