In paragraph 2, Daniela has "an even louder bow arm." What does this phrase most likely mean?

Ana Lucy had played second violin in the Río Vista Middle School mariachi for two years, and she knew every part of every song. She knew the first violin part best of all, because she had spent most of seventh grade hearing it played slightly wrong.

The player who had it wrong was Daniela Garcia, an eighth grader with a loud laugh and an even louder bow arm. Daniela rushed the fast passages, and in "Cielito Lindo" she always played the high note a little flat. Ana Lucy never said anything. She played her own part carefully and waited.

Now Daniela had moved to Laredo, and Ms. Gonzalez was holding auditions for first violin.

Ana Lucy practiced the solo from "El Son de la Negra" every night for a week. She practiced until her fingertips ached and her little brother started humming it in the shower. On the morning of the audition, she could play it with her eyes closed.

Then Ms. Gonzalez handed her a sheet of music she had never seen.

"I already know you can learn a part," the teacher said. "I want to know if you can lead one. Play this the way you would want the rest of the section to play it."

Ana Lucy stared at the page. Her mouth felt dry. For a moment she thought about Daniela, who had never once looked worried, even when she was wrong. Then she lifted her violin, took a breath, and played the first line slowly and deliberately, loud enough to be heard at the back of the room. She missed a note in the third measure and kept going without stopping.

When she finished, Ms. Gonzalez was writing something on her clipboard.

"You hesitated," the teacher said without looking up. "Then you stopped hesitating. That second part is the one I needed to see."