How to structure deal with sister - buying a duplex

My sister is a first time home buyer. We are looking at buying a duplex together. She would live in one side and we would rent the other. I am co-signing the loan and probably putting up the down payment. She will get the loan so she can get bett terms than I can as an investor. How should we structure our deal so we are both protected and get a fair shake?  Not that we don't trust each other, just better to have it all set up from the get go. No surprises on the back end. Thoughts?