Thank you all for the feedback and information. Just to clarify, we both signed the deed of trust to hold the lot and make the payments. I agreed to pay her back all the money she has put into the house since I believe that is fair if she is pulling out. However I do believe its not fair of her to pull out in the first place since she did sign the deed of trust, but that was our fault for not having written agreements that cover all possible situations. The one written agreement we do have is very vague and states she will receive her money back plus $8,000 per year of living together upon separation- however we have not begun to live together since the house isn't finished.
We have a friend of the family who is a retired lawyer and I spoke with him very briefly a few months back. Regarding the lot, he said since we don't own it she isn't entitled to receive any interest payments back, but she is entitled to get back any down payment she made.
If she's requesting to get interest on her money on top of the interest payments made wouldn't it make more sense for my parents to request interest on their money they have loaned us since they have nothing to do with the house other than the loan, then split that amount between the two of us.. In that case whatever % interest rate she would want it would technically get cancelled out with the interest from the loaned money since it was double the amount my girl friend contributed.
We've been discussing everything and my parents want to make things as fair as possible that's why I wanted to seek some advice and hope that it doesn't come down to having a legal battle.
Thanks again, appreciate all the feedback