I am a US citizen who used to teach in Georgia and am now teaching in China...

If I were to send a personal invitation letter to a Georgian friend (she is currently a student at Tbilisi State Uni, who has a valid passport and is over 18 yrs old), what other documents would she need besides:

Visa Application,
A current passport photo with light background,
Copy of passport signature page,
Copy of personal invitation letter,
Visa processing payment

I fear purchasing an airline ticket only to have her visa be denied. She would also be staying in my spare room so no hotel reservation would be made. What are her chances of coming to visit for 7-8 days? Do you have any recommendations?