Why is she doing this to me?

my girl is in jail for three weeks. i visit her once a week. i sent her a letter the first week and didn't hear anything back. i went to see her again and she told me that she needed money to buy the supplies to write a letter in jail so i sent her some money to write me with. she promised she would so i was cool with that. i was suppose to get her letter three days ago but i still don't have it. do you think she just doesn't want to write to me or do you think i'm worrying over nothing?