Absolutely. I definitely did tread too carefully. That said, every time I did ask a probing question (e.g. "how was your weekend, did you do anything fun or exciting?" -- by the way, that's almost a verbatim reflection of a question that she asked me once), I always got a non-answer, like, "oh, it was just a normal weekend for me". And she never used plurals -- we/us/our/etc. -- always the singular -- I/me/my/etc. So I was paying attention, I just think she doesn't talk about her husband.
I also feel that because this is the workplace, I do need to tread more carefully. I ruined the workplace environment for a woman once about 20 years ago, just by letting her know that I was interested in dating her (at the end of the -- in my mind -- first date). I had the decency to feel bad about it, but it makes no difference to the woman, it was still ruined for her. I promised myself then, that I'd never do that to anyone else ever again. They spend just as much time in the workplace as we do, 8 hours a day...half their waking life during the week, but because of the lopsided man/woman dynamic, there's no equivalency. They deserve to feel safe, comfortable, and free to be themselves. I have become a hardline feminist in that regard.
That said, I was correct that she wasn't interested, so I did get that right, it just wasn't for the reasons I thought.
She was fairly pleasant with me today, so she's being more of an adult than the woman of 20 years ago. She's still one of my favourite people, I've never met anyone else like her, and I am glad that I will still be able to interact with her, if a lot less so.