First of all, I don't know anyone involved in this transaction.

Yes, the monthly mortgage payment is less than the income she previously had. 
How many tens of thousands of dollars is she not paying in property taxes every year?
How much maintenance is she not paying every month?
How much insurance is she not paying?
People don't realize there are costs of doing business. The $6500 per month is far from pure gravy. She now has a steady income that will most likely last longer than she will with no worries.