I think the first thing to do is to not panic, or do anything hasty.
Contact Cinderella and ask what their procedure is for dealing with complaints about the services provided by one of their practitioners.
Wait for their reply.
In the meantime go and see an independent extensionist and ask for their assessment of the hair. Do not mention anything about who/where you had this done, or the circumstances. Let them tell you what they think. Take a witness. Make notes.
Ask them to take photos. They may refuse because they may feel it gets them getting involved. You may have to pay for an independent assessment. Get a receipt.
Write a letter, recorded delivery, to this girl with the photos.
Be factual, no opinions, but you can tell her that this was not what you expected of the treatment.
Ask her for her insurance details and then correspond only with the insurance company.
Do not text/phone or otherwise contact her after you have involved the insurance company.
I wouldn't advise trying to "sue" her. All the money in the world will not make your hair grow faster.
I'm guessing that what you really want is your hair in good nick for your wedding. Any financial compensation may be able to pay for new extensions.
Take a deep breath and stay calm. Your hair will grow back!