This morning my boss was in a meeting room with 2 other managers and I went to ask if they wanted coffee/water. As I approached to knock, I could hear my boss telling the others that I 'just sit on my arse and don't offer to complete checkouts' and then 'ridiculous notion that she wants a payrise when she can't even do the job'. I immediately left & went back to my desk in shock. I had my review last month and she mentioned none of this: it was all very positive.
I wanted to find the courage to speak to her about what she said as it's really making me feel very unwanted and useless. On the other hand I feel bad for even overhearing - I stayed to let her finish - in the back of my mind I even wanted them to see I was at the door (it's part glazed).
Is it unreasonable/unadvisable to approach her privately and ask about this?
Should I just put a brave face on it and let it blow over? She often talks badly of other staff/contractors/clients instead of telling them what she doesn't like and giving them the opportunity to improve, and when I think about it like that, I guess it's not such a shock. But I considered her a friend, listened to her worries, cheered her up and told her she's doing a great job (she is, otherwise), and it feels very hard to hear her slag me off to others, and not mention any of this to me directly.