I am a mother of a 5th grade girl who has struggled greatly with dyslexia. I am also a Special Education teacher and have participated in many dyslexia trainings and have researched dyslexia at length. With that said, here is my advice.
Even though I am a public school SPED teacher, I am the first one to admit that our public schools do a terrible job at meeting the needs of dyslexic students. The schools know that one out of every 8 students have a learning disability, but they provide little of the research based techniques that will help these kiddos. I actually put my daughter in a private school this year (Rawson-Saunders in Austin, school for dyslexics). Of course, the private school takes the majority of my pay check each month, and would probably be too much for a housekeeper's salary. It is a shame that public schools cannot provide these children what they need.
My advice, she needs to be a squeaky wheel at his school, if she meets the teachers face-to-face with her concerns, they(the teachers) will remember her child far above the other 200 children coming through their room that day.
If his modifications are not being met that would definitely cause him to fail and feel very unsuccessful. Dyslexics are smart and just need different ways of learning. He may need notes copied for him and shorten assignments. Mom needs to make sure she is attending his 504 meetings at school, and she may need to request another 504 meeting in order to get a better understanding of the demands placed on him and the modifications that will best help him. Mom needs to educate herself of the modifications available because the school will not be forth coming with suggestions (as it is usually more work for the teachers involved).
Just because modifications are put in place does not mean the school teachers will follow those. It is an ongoing responsibility of the parent to stay in touch with the teachers and student to ensure he is receiving these modifications. She can also educate her son on the modifications and encourage him to become his own advocate as well.
Modifications that should always be included for severe dyslexics; math tests given orally (in order to test his math skills not his lack of reading skills), hard copy of all overhead, chalkboard, and classroom notes, shorten vocabulary or spelling lists, shorten reading and/or essay assignments (he can still learn the core of the assignments, but very lengthy assignments are beyond overwhelming and exhausting to a dyslexic), testing should take place in the content mastery room with questions read to him.
There are also modification requests such as audio tapes for textbooks, spell checkers and dictionaries allowed.
Importantly, he needs to know that he is not "stupid" and that most dyslexics shine in other areas of creativity, athletics, and the arts. Thomas Edison and Isaac Newton were dyslexic, it is important that he knows some of the smartest people in the world are dyslexic.
Again, his mother needs to be his biggest advocate and ensure he has what he needs through the public schools to ensure his success. She should contact the Content Mastery teacher at his school and develop a relationship with those who can provide him extra support.
The dyslexia school in Austin, Rawson-Saunders, does provide consultations and could help her come up with the best modifications for him. It may be pricey, but life changing.
Thanks and good luck.