When we "just sit," we "just sit"
... we let thoughts go without analysis during Zazen. There is nothing to do or attain in the sitting, nothing to examine or focus on ... and that non-doing and non-examining is VITAL.
Now, on the other hand, I think her "thought labeling" recommendation is a wonderful thing to do at other times in daily life
, as thoughts arise during our busy day ... when tired, hot, a little angry, happy, etc. I also advocate the practice of labeling, just not --during-- Zazen itself (when we are not to be adding anything). Labeling is, however, a very important part of learning to observe our mind's workings. So, for example, instead of just feeling angry, greedy or tired, and instead of just saying to ourselves merely "I am feeling angry/greedy/tired now), we should learn to say to ourselves such things as "this is my mind now temporarily feeling angry/greedy/tired during present conditions ... I can feel it arising, I can feel it developing, I can feel it passing away". When we learn to do that, experiencing the emotions of the mind becomes just watching a bit of theatre.
All that is good, just not a practice for "during" Zazen, when we observe everything and nothing.