Private lenders offer fast approval and flexible terms compared to traditional banks 

They have been approved for a single family home Fannie loan (cannot do FHA because my husband works in the Cannabis Industry and the gov't will not allow).

And once you've got an approved applicant, then you present them with your lease, which needs to be comprehensive in its protection for you and of your property (mine is 24 pages and counting as I encounter new issues, and it contains fines for certain violations) - check your state laws.

We are allowing her to find someone to replace it and save money as long as they are licensed and we approve it.

I would advise you to approve this applicant unless there is a strong, objective reason not to - such as eviction history, a recent criminal conviction, or their income (including all disability income) is less than whatever standard you have used for all of your past tenants.  

I've been approve by the bank and they are willing to loan 80% of the money, but I need to come up with the 20%.

Such as storage, RV park, Mobile Home Park, etc. 

He said I need to get a signature on a 'notice to vacate' from one of the tenants to even be approved for the loan.   

@James Walker I would start with planning and zoning, assuming you've done that part and/or feel likely you can get it approved, then I would pay for a feasibility study from a neutral 3rd party. 

I would be very interested in your experience interviewing with brokerages and what you find.I have already applied for my license and way approved on inactive status, but I don’t think it’s necessary.