No it is not hers if they dont correct it, that is absurd. Nor does she have any right to touch the interest. Period.
Tell her company and if she wants to, tell everyone in writing but this will be corrected soon. Do NOT transfer that extra money or touch it, interest, or anything else to do with the extra money in any way shape or form.
Just my OPINION not meant as legal, accounting, or any other advice to you or your daughter.
Eventually it most certainly is hers. The time period seems to vary by state, but indeed all the legal sites I just checked all said the same thing, eventually it’s your money and if they do catch all you owe them is the error NOT any extra you might have earned with it (like interest in another bank) while they were getting their act together.