Otsukaresama (お疲れ様）

So the wife sometimes calls me at work in the middle of my day. I'm doing my thing, while she talks to me on the phone about something. (Yes I am paying attention) She asks if I am still working, I say, "yeah" and she proceeds to respond with "Otsukaresama"... Now mind you, I am second generation Japanese born here in the US so I consider my Japanese second rate at best. My wife is 1st Gen born and raised in Japan.

To me it sounded strange for her to say "Otsukaresama" to me while I'm working... To clarify, "Otsukaresama", from my understanding, is used after you've finished something. It's a term that is used to acknowledge someone's efforts or show your appreciation for the trouble that they have gone through. So I mention to her that is sounds strange for her to use "Otsukaresama" while I'm still working. According to her, it's used to show appreciation for the work I am doing... Still, even after she said that, it feels strange for me to hear the term used in a fashion that I've never been introduced to.

I'm calling shenanigans on my wife!!! (hahahaha, just kidding wife...she is so going to kill me) In all seriousness though, I simply want to make sure I sound intelligent in conversation in the Japanese business world if I were to ever be presented w/ the opportunity. So because it sounds strange to me in her usage, I need that confirmation.