Open title, get an inspection, and get a quote on property insurance. Are you going to get the loan in your personal or business name? Also is she going to use her name, trust, or business as the lender?
Find out how much money she wants to get a month and go from there. If she doesn't want to hold the note for a long time, you can do a balloon payment. I don't offer a down payment nor an interest rate unless they want it. For example: 100k paid off in 10 years.
Use a loan servicing company. It looks more professional plus it protects both parties. I just set one up with Secure Net Loan Services. I can't give you a review yet since I've never used them before. It cost $125 to set up and $25 a month. Google loan servicing companies and you will find more. Give
The title company's lawyer can write up the note and deed. I think mine cost about $900. If you plan on doing more real estate, try to use the same title company every time. Familiarity is important.