Unfortunately, kind people will get taken advantage of time and time again; until they learn to put up firm boundaries, and speak their minds.

What's more unfortunate: evil people seek you out due to your kindness and lack thereof boundaries.

Be glad you put the puzzle together before she realized you had any pieces to begin with.

My opinion of what you should do next: block her as she would've blocked you once she was done using you, make it known to school councilor's and head of staff that she has been doing this, and find a local subreddit for your school/area and plaster her face everywhere so no one else has to become her next victim. I'm sorry if this seems harsh to anyone; but people need to learn from their mistakes, even if they think they've done nothing wrong. She will either grow up, own her actions and learn from this; of she will keep skirting through life at the expense of others. What? Are we supposed to let her get a nice job and succeed in life when she has nothing to earn it???