Home Equity Share Agreement

My wife and I helped our daughter purchase a condo.  We put up 20% down payment and have been contributing towards 20% of the expenses.  After the fact, I learned we should have a written Home Equity Agreement and that my daughter is supposed to be paying us 20% of the fair market rent which we would then use to pay our 20% share of the expenses.  Seems silly, but the IRS requires a rent payment if we want to take any deductions on our 20% of ownership as an income rental property on Schedule E.  To complicate things, my daughter rents out a room.  Does she need to pay us 20% of this rental income, or can that be treated as her separate income and she would then depreciate her 80% of the property value?  

Next question, what happens to our write deductions if we stop contributing towards 20% of the expenses at some time in the future?