name it or guess what Stargirl might call the game, I would call it the "Empathy Card Game." The chapter begins with Stargirl telling Leo where she gets her information about people and what they might need to make them feel better. She reads the "filler" sections of the newspaper. She eavesdrops on conversations at places like the hair salon, and she reads bulletins boards around town. Stargirl then asks Leo if he wants to play "a card game." Leo immediately knows that she isn't talking about a game with an actual deck of cards. He agrees to play, and Stargirl explains the game to him.

She poked me. “Hey, want to play a card game?”

I had a feeling she wasn’t talking about poker.

“Sure,” I said.

She said she invented it. “All you need is your eyes and one other
person. I pick somebody on the street, the mall, a store, wherever, and
I follow them. Say it’s a her. I follow her for fifteen minutes, not a
minute more. I time myself. The game is, after fifteen minutes of
watching her, I have to guess what kind of card she needs.”

Leo likes the idea of the game, and he agrees to play it, but he is confused about how to get the cards to the person if they don't know the address. Stargirl explains that the person is never sent an actual card for that reason, and that is why it is only a game.

“But how can you get it to her?” I said. “You don’t know where she
lives.”

“True. That’s as far as it goes. That’s why it’s just a game. It’s just for
fun.” She snuggled into me. She whispered in my ear, “Let’s play.”

In the book Stargirl by Jerry Spinelli, the character known as Stargirl likes to play a game at the mall and in other places as well. She picks out a person, and she follows him/her for fifteen minutes. After watching the person for that amount of time, Stargirl guesses what kind of greeting card she/he "needs." Stargirl gets Leo to play the game with her when they go to the mall. Together they pick out a woman they assume to be in her forties, and they follow her as she buys a soft pretzel and goes into a video store where she asks for the movie When Harry Met Sally, which the store does not have. The woman then passes by the Sonoma store, but goes back and enters. Stargirl and Leo watch her as she touches pottery and picks up a plate with a "French cafe painted on it" (Spinelli 115). 

After they follow the woman for exactly fifteen minutes, Stargirl tells Leo what she thinks is the woman's story:

"'Well, she's divorced and lonely. No wedding ring. Wants somebody in her life. A home life. She wishes she were Sally and her Harry would come along. She would make him dinner and snuggle with him at night. She tries to eat low-fat foods. She works for a travel agency. She took a free cruise last year, but all she met on the boat were creeps. Her name is Clarissa, she played the clarinet in high school, and her favorite soap is Irish Spring'"(Spinelli 115).

The card she would send her is a "While-you're-waiting-for-Harry-be-good-to-yourself card" (Spinelli 115).