Can't believe a health care worker would pull a mask below their nose! I do see it below noses all the time. Sigh. It's tempting as I often can't breath. I take breaks and pull it off for some fresh air as I can't wear it continuously. But wearing it below the nose isn't too helpful, is it? But, as stated, I doubt you'll get sick from that interaction. Mask shaming is the new thing. I don't really like that either. But I do wish everyone would comply.
A very low chance. She is most likely not sick. Also it takes minutes of face to face conversation for enough particles to be expelled to cause risk, and you were masked.
You were well protected, so even though she pulled her mask down, it's not likely that you could get it.
Did you ask her to put it back on? Don't ever hesitate to advocate for yourself.