Exactly the same happened to us.
Wife and I ate at the place out daughter worked, I left a decent tip for her.
She had told us not too. Didn't feel we should tip her.
When she didn't mention it for a couple days, I ask. Someone stole it.
Maybe a 10th of the OP, but a good lesson for her.
She learned to cruise past the table if someone was getting up.
She bussed her own tables so it was a waitress or customer.
