Thanks for responding. All good questions. Here's more of an explanation.
We weren't that close as friends. My cubicle was next to her cubicle and we did chat at times. I was the new kid on this particular block. She was always nice, helpful and courteous to me. My job has almost nothing to do with her job.
The mutual friend said that fired person feels devastated that she'd worked at a place for such a long time (over 20 years), she's gone in one day, two days later someone else is at her desk, and no one says anything to her. I can understand how awful that would feel.
There has been a bit of talk about it and there's a level of ambivalence. To summarize: people genuinely feel sad that she lost her job but there's also an understanding that she did not help herself in this situation. So no one really knows what to say.
There's a part of me that understands her devastation so I want to somehow commiserate with her on a human level. But I feel like I was someone more on the periphery of her work life (ex: we never had lunch together) and I was not a personal friend and probably would not have formed a personal friendship with her.
I asked the mutual friend what she wants me to say and she said, "Just say hello and tell her that you'll miss her." Mutual friend is a personal friend of fired person and she feels terrible although she also knows why it happened because she knows all the details, much more than I know. I still work with mutual friend and she and I DO work together a lot so I do worry that she'll be annoyed with me if I don't call. And I like mutual friend and she and I have more of a personal relationship. Yes, I'm totally aware that mutual friend is putting pressure on me but I honestly believe she is doing it because she, too, is horrified at how quickly one can disappear.
The way I see it now, I have to decide which is worse: my one-time discomfort with a phone call or a longer term antagonism with someone I see daily. Not a great choice. But in this real world, if I need to choose, I'll make the phone call.
So THAT's why I want some advice on what to say.