Couldn’t they use her Twitter post against her?
They could but it still isn’t proof that she did it.
However, she is probably mentally-challenged (especially after that message) and doesn’t realize she’ll leave DNA which will prove what she did. And DNA testing is relatively-cheap these days.
1) Track her IP, or offer a reward - she can’t be that hard to find
2) find her employer,
3) get the undercover restaurant people,
4) put her in prison