I can understand your concerns fully with sister. The biggest challenge to having dyslexia is the way that people deal with the person because they have this difficulty in something that is extremely valuable and appears to be taken for granted by persons that read/write with ease. Dyslexic people will have a very challenging road based on improving an area that they must face on a daily basis for the rest of their life.
It is very sad that people that have limits and difficulties due to dyslexia are treated so poorly. As humans, we must look and be willing to promote a wider understanding of dyslexia. As parents, students, family members, friends, and teacher; we must be tolerant and willing to offer assistance on how to help dyslexic people learn and work more effectively.
Please look for help groups in your area and online, your sister is not alone, many people both old and young share the same difficulties daily caused by dyslexia.