Did you ever end up talking about it later? The apology? Maybe she's uncertain, if you aren't opening up to her, more? A little vulnerability can go a long way, I'd hope?
Sure, work is stressful to her, but it seems there's more beneath the surface of it all. Almost crying at work, sounds like she's riding some personal roller coaster, at the moment.
Maybe, by opening yourself up, she can open up more than just work related stuff? I am not sure, I can't get a good read on this....