Just for verification.
1.) When you say "she gives all of my monthly payments to the lending company as her payment to her loan" Should you mean that the debtor has the access to you financial details?
To answer you question "how could that be when I am not a party to that particular loan?? I didnt personally applied or made myself a guarantor for a loan in their lending company?
That could actually be possible even if you didn't oblige your self as a guarantor, if NOVATION took place. Novation took place if for example; X owes 10,000 to Y, with the knowledge or consent of Y, Z oblige himself to pay the indebtedness of X. Therefore, the acknowledgement of Y to Z as a new debtor, extinguished the obligation of X (Art. 1293 civil code)
Meanwhile, this is the only reason that i can see why you receive a demand letter from a lending company instead of your friend who went abroad.