@mydarlingwhatifyoufly
I wouldn't personally. Not because it's anything other than a game, but I can imagine (if she uses it with friends) that a group of teenagers could easily wind each other up and one or more could end up really scared or upset.
This puts me in mind (a bit) of a little game a group of people played at my DH's workplace some years ago...
They all wrote 'I sell my soul to John Jones, for a pound, and he is thereafter the owner of my soul...' Then they signed the document, and he gave them a pound, and a small handwritten receipt. (It was after the episode of The Simpsons where Bart sold his soul to Milhouse and got really upset afterwards, as he realised what he had done, and he desperately tried to get it back.)
Some people were laughing at how dumb it was, and how there is no such thing as 'selling a soul' and so on...
So 'John' made up a little game where these skeptics who were mocking 'sold their souls' to him.
5 men did it. Within an hour 3 of them were asking for the piece of paper back, and offering the pound back, saying they felt uneasy and weird about it. John said 'no, your soul is mine now....' with a sly, 'evil' glare.
The one guy (Dave) started to get very upset and worked up, and John still said no. It got into a big argument and 'Dave' actually started to cry. 'John' was stunned and said 'Jesus man, just have it back, you said it was all bollocks that a soul could be sold anyway!' And he took his pound back.
During the day, all 4 of the others went to him and asked for theirs back too.
Weird, as they were all so skeptical.
As you said, even though many people are very skeptical about this kind of thing, but deep down, when they really start to think about it, many people will get freaked out.