Triplex Deal Structure? HELP!!

[Bowman Harvey]

I am an investor in the seattle Market. Me and a partner formed an LLC. We recently found a triplex that will cash flow 500$ a month in Seattle proper. Not having the income or the credit to qualify Me and my partner asked a wealthy family member to put up the 30 percent down payment, purchase the property in her name. Which she did.

         This angel investor doesnt ever want to step foot on the property doesnt want anything to do with it other than just a stable return on money.  So I am thinking of offering her a long term private loan  at 8 percent untill the loan is payed back.  She wants something in writing, my question is what would this type of arrangement be called and where do I even start with structuring this?

Here is what i  have done:

1)have an LLC that Tenants will write rent checks to, mortgage payments will be on an automatic withdraw from this account and then the cash flow after all expenses will go to pay the investor the loan

2) the LLC has an operating agrement between myself and my partner

so do I need a seperate "operating agreement" for this particular triplex?  the investor wants to know who will e doing everything right down to who is  mowing the lawn.???? this closes in 2 weeks and understandably the investor wants this done soon after closing any thoughts from you guys on how to put this deal in writing?