Hi,
I don't know what the Embassy will look for, but I would guess you should include at least the following information.
Length of stay in the USA, including planned or suggested arrival and departure dates.
Address she will stay at.
Purpose of visit.
Your relationship to her.
Perhaps a statement of your intention to be responsible for her if any financial problems arrive?
I imagine the Embassy's concern is to ensure that this is a genuine visit and not just an excuse to come and not leave again.
Best wishes, Clive