Hello, my name is Judith. Thank you for this opportunity to answer your questions.
There is nothing you need to do.
The visa applicant has the burden of proving they have compelling ties to the Ukraine that will draw them back after visiting the US.
The consul looks at their age and marital status, whether they hold a professional job and have been employed steadily for a significant period of time, whether they own or rent their residence and have other financial ties to Ukraine.
One of the reasons they have to show they have financial ties is to prove they have the ability to support themselves while in the US.
You can issue her an invitation letter and an Affidavit of Support. However, that would absolutely kill the visa application because the consul will assume this is a romantic relationship and she is coming here to look at marrying you. The appropriate visa to do that is the fiancé visa, not a visitor visa.
Most often gentlemen who have girlfriends abroad make the trip there to meet them because the visitor visa is refused. If the personal meeting goes well they come back and file for a fiancé visa.
Be careful sending her $800 in traveler checks because the visa most likely will be refused and she then has your $800. Of course, if you want to give her a gift of that $ and understand it most likely will be a loss to you, that is your option.
B1/B2 visa applicants must "demonstrate permanent employment,
meaningful business or financial connections, close family ties, or social or
cultural associations, which will indicate a strong inducement to return to the
country of origin."