Sobbing
a : to catch the breath audibly in a spasmodic contraction of the throat
b : to cry or weep with convulsive catching of the breath
In the context, the word sobbing means: that Denver had difficulty speaking. She was probably crying and she lost her breath.
“But Denver was shaking now and sobbing so she could not speak.” (P.9 line 4)
Source: http://www.merriam-webster.com/dictionary/sobbing
Does this give you a sense of whether she was crying softly or very hard? Your explanation could include that information.
The general meaning of the word SOBBING is: crying hysterically. The quote I mentioned wasn’t enough to show if Denver was crying softly or hardly. I went back to the passage and read it again and found out that she was crying very hard according to what the author says in the same page “The tears she had not shed for nine years wetting her far too womanly breasts”. It is noticeable that Denver was crying hard and for a long period of time.