Tenant Screening - Previous Subletters

[Michael S.]

I have an applicant that listed a single previous residence on her application. After calling the previous landlord, I discovered that my applicant was not on the actual lease with the landlord, but was likely a subletter of one of the lessees. Previous landlord can't release details about someone for which I don't have a signed authorization. My applicant may or may not have ever been on a lease personally before. 

Do I just treat her as if she has no previous rental history? 

Try to get authorization from the person she sublet from? 

What do you guys do in these situations? I'm eager to fill this vacancy, it's been ~ 2 months, but I don't want to rush into a situation with a bad tenant.