Why is Brigid slowing down at work in chapter 15 of Lyddie by Katherine Paterson?

In Chapter 15, Mr. Marsden, the overseer, complains to Lyddie that Brigid is too slow in her work. He tells Lyddie that she must make clear to Brigid that she will lose her job if she doesn't pick up her pace at the looms.

Lyddie tries to warn Brigid, but the young Irish girl seems too upset to take much notice. However, she perks up when Lyddie offers to work on five looms together with her, for a few days. With Lyddie's help, Brigid improves slightly. However, she eventually starts to slow down again. When Brigid almost ruins a piece due to her inattentiveness, Lyddie yells out in frustration at the quivering girl. Brigid finally admits that she is worried about her mother, who is very sick. She also confesses that her worries stem from the fact that they have no money to take her mother to the doctor.

Upon hearing this, Lyddie gives Brigid some money to take her sick mother to the doctor. Brigid is so grateful for this gift that her work steadily improves.

She beat Lyddie to work in the mornings and had two of the machines oiled and gleaming before Lyddie even entered the room.

Why is Brigid slowing down at work in Lyddie by Katherine Paterson?

Brigid slows down because she is worried about her sick mother.

Brigid is one of the newer Irish factory girls.  Lyddie spent some time helping the new girls learn how to work the machines, but she has little patience for them.  She is too focused on her own work.

One day, Lyddie looks over and notices that Brigid is crying.  She decides that Brigid needs to “bear her own troubles.”  She doesn’t intervene.  She has her own problems, since she is worried about her little sister Rachel. 

Then Mr. Marsden, the overseer, asks her to do something to speed Brigid up.

But it was not about Rachel that Mr.  Marsden wished to speak, it was about the wretched Irish girl.

"You must tell her," he said, "that she must get her speed up. I can't keep her on, even as a spare hand, unless she can maintain a proper pace." (Ch. 15) 

Lyddie is a little confused that Mr. Marsden does not just tell Brigid himself.  After all, it is his job as the overseer.  Brigid looks so frightened when she tells her that Lyddie feels sorry for her.  Brigid reminds her of Rachel.  That is the reason Lyddie agrees to help her. 

Unfortunately, Brigid is slower than ever, and Lyddie wants to scream.  She finally asks Brigid what is going on.  It turns out the girl has been worried about something. 

At last Lyddie exploded when once again the girl's inattention caused a snarl and a ruined piece. "You must mind, girl!" she shouted. "Forget everything else but the loom." 

"But I canna forget," Brigid cried out. "Me mother sick unto death and no money for a doctor." (Ch. 16) 

Lyddie gives her money for the doctor, and things improve.  Brigid is actually early to work, and eager.  Lyddie finds her “pathetically grateful,” but she is glad that Mr. Marsden is pleased.  Unfortunately, Lyddie becomes ill.