I filed for my Mother-in-law and now need to respond to a letter

I filed for my 95 year old mother-in-law and she received a 4883C letter.  Do I need to have her complete a Form 2848 to resolve the issue?  If so I do not have a CAF or PTIN  number that the form is asking for.  What are these numbers and how do I complete the form without them?

 

Thank you.