I think you made a mistake from the scratch, paying her very well from the start.
She could have thought two things out of it: either you are very generous and she respects that, or that she can take advantage of you.
I pay my maid above the standard rates (not by much but still, 15/20% higher than the average), but I started with a standard rate. Then later, she found 5.000 USD I had in cash (had forgotten to hide them) and she didn't touch them (if she had stolen them, I had no proof she had stolen or that this amount actually existed). That's when I decided to pay her well.
I would make sure she doesn't take away a "gift" that she considers a "due" the day she leaves.
A friend of my GF would be happy to submit her candidature (she has experience, is 19 y/o, best friend of my GF, she slept at my house a few times too with no issue).