Tenant Prospect Payment to not market my property

[Christopher Melvin Brandy]

So I have a prospective tenant who has a section 8 voucher.  She won't be able to get a new voucher until July 1, 2019 which is a month and a half away.  She desperately want to moving into my property because it's a 4 bedroom and she qualifies for a 4 bedroom.  The Section 8 process and inspection may run throughout the month of June.   She's paid the full deposit of $1500 so I removed the listing.  I told her that if the housing inspection is not complete or doesn't pass inspection by 5/28/2019, I'd refund her deposit and find another tenant.  

She believes the section 8 process may take run throughout June and they won't pay June's rent anyway because they're already paying the rent at her current residence.  She offered to pay June's rent out of her own pocket without taking possession of the property or signing a lease.  Essentially the $1500 rent payment is a gift so that I won't market or rent the property to anyone else until July.  I won't be giving her the keys or signing a lease for June.  If the section 8 process is is complete by July 1st, 2019, we'll sign a lease and Section 8 will pay the rent going forward.  Is this legal?  Am I at any risk?  How can I document this agreement?  Should I document this agreement?