I'd be in the car driving to starbucks..heheh!!
It will teach her that if she does happen to come while your gone and she calls you asking where your at you can tell her well we did wait for 45 min with no call so you figured you had the day off. If she said she would of called first to tell you that she wouldn't be coming you can inform her that she didn't call nor did she call that she would be late and for the future that if she plans to be late no matter the time...she needs to make that call as a courtesy...