Melania expected a lot worse.
The people she saw on a daily basis would've reacted to such a proposition completely differently.
If she offered to do anything to repay the favor she was given, then their minds would immediately go to places that would end in her exploitation.
August was different from them. She'd seen this from his behavior and the fact that her siblings liked him. Deciding to trust him was a leap of faith on her part, but she felt it was the least she could do after what he'd done for her.
So she said it. She said that she would give him everything if he asked for it.
And for him to just say that he wanted to be friends…
She wanted to laugh at herself for worrying in the first place.