Raising rent and eventual sell to section 8 tenant.

[Krista Moreno]

I have a tenant who’s on section 8. She pays just over $300 and section 8 pays almost $900.  I’m only charging her $1200 and could probably get closer to $2000. It’s a 3/2 in central FL. She pretty much begs to not raise the rent and wants a lease for the next 4 years. Then once her car is paid off she wants to go through the section 8 program to buy my house, which I wouldn’t mind if she doesn’t low ball me because I could then invest in other properties. Should I (& how much) raise the rent. And any idea how the selling of the house to her would work and if it’s a good idea? 
Any thoughts and suggestions on the matter would be greatly appreciated.