My sister does not have good enough credit or income history.

In the book Millionaire Real Estate Investor, the author has a number of investor vignettes.

Low maintenance property with minimal maintenance history, good occupancy. 

If you can work with the monthly payment today, history says that your interest rate will only go down over time (if you stay tuned in to the rates).

Some people do well with second chances.Here is an excerpt from our screening criteria, which is more flexible than some....LEGAL/CRIMINAL HISTORY1.Criminal offenses (misdemeanor or felony) of a violent nature against either person or property will result in denial.2.Applicants with a non-violent criminal misdemeanor that occurred more than two years ago or a non-violent criminal felony that occurred more than five years ago may be considered if restitution for their crime was made in full and all time was served.Also, we may require an additional security deposit and demonstration of good employment history, credit history, and rental history since the time of the crime.Multiple offenses may result in denial regardless of what the employment, credit and rental history shows.

My working history during this time have been inconsistent and unstable, but my credit history is still pretty stable. 

Believe it or not, this happens.You should obtain a credit report and eviction record search to see if these applicants have a history of breaking their lease and/or leaving property damaged.

When you go to sell it with less than about 12 months of  income and expense history you will be limiting yourself to buyers that have access to more cash and/or better financing.  

This can be different dependant on your credit history.  

If you currently have a mortgage on your existing house most mortgage lenders will not allow rental projections only a seasoned history.