Nope - don't buy it.
I would NEVER use someone else's food...and if there is something unusual in the company fridge from what we normally have, I ASK if it's something that the company has provided (I did this about mayonaise just last week actually, turns out it's provided as our client is Helmanns)

Then again - if it had been anyone else, I probably wouldn't be so fussed and just sent them a little email. But this is my ASSISTANT who I am doing her work as she is too stupid to do it herself. Or feels it's beneath her or something like that.

Sorry - rant over - for now...I am sure she will piss me off again.