1) Does the youngest have any close friends? If so, do what you can to encourage this, especially if they go to a different school. Having some close friends will probably make the rest of school suck less. If not, I'd really consider encouraging her to hobbies to make those friends. If you can afford it, consider letting her do summer camps or lessons in a variety of things until she has one thing her sister doesn't, and maybe she'll make some friends along the way.

2) You said she had dyslexia. Have you gotten her tested for other things like dyscalculia or dysgraphia? Knowing what will be struggles and finding ways to counter act them early might not be a bad idea. If there is dysgraphia, GET HER A COMPUTER. SPELLCHECK IS AWESOME.

3) Consider looking into tutors. Teachers with 30+ kids are going to have to present the material for the majority and might not even be taught how to handle autistic folks in the best of cases. Bribe child with pizza and clothing money if needed.

4) Introduce yourself to her teachers. Chances are, at least one is going to be a bully. Nip that in the bud by speaking to them.

5) Make time through your work (Or your wife, doesn't really matter which) to scream at people. When my very bullied sister got to school, my parents often had to head to the principal's office to sort out things. Be polite, but make it clear you will not tolerate a teacher or student bullying your child and that they aren't going to get rid of you easily.