Clauses

This is from a novel called "Cold Moon:"
"Sachs ignored the clerk. She didn't want to give her the satisfaction.Through the nondescript halls, turning corners here and there, not saying a word. Sachs struggling on her arthritic legs to keep up with the man's energetic pace. "

My question to you is as follows:
why did the author use the continues tense to describe how Sachs was walking instead of saying "Sachs struggled on her arthritic legs to keep up with the man's energetic pace?"

What is the legitimacy of using clauses?

Looks like bad grammar to me.

prosal license I guess

I rather like it despite it being bad grammar

it mimmicks one's (a character's ?) erradic thoughts....