@Chelsea ******
Yep. Your boss just seems determined to show even more definitively why she'd be an awful, toxic person to work for, by outright lying to you like that and trying to menace you. She knows damn well that the initial visa cannot be cancelled, only the extension. If she says otherwise (that she honestly thought otherwise) I'll call her a liar to her face. Shes experienced in the field of employing foreigners, theres no way she doesnt know.
The only response she deserves is to be told to shut the fuck up & go play on a busy road.
Preferably a *Thai* road.