One thing to keep in mind on processing speed is that you CAN improve it with practice. My son got a 99% on just about every part on the WISC except PSI which was 40%.
For the last year, we have been doing flashcards and occasional timed math tests. (For some reason, thank goodness, his class isn't doing timed math tests but I'm sure they will come back). I think he's maybe in the top 1/3 now on the timed math tests- OK, not great, but ALOT better.
You can improve these skills by practice.
Whether or not you can improve the skills that are reflected in the subtest processing speed depends on the reason they were low to begin with. Some kids, like my ds, have neurological disorders which impact their ability to do those tasks and which no amount of practice will significantly improve. They might improve incrementally, but remember that every other neurotypical child is also seeing an increase in ability to do timed tasks as they mature too and that's reflected in test norms.
Please know I'm not saying you shouldn't have your child practice to improve skills, and I don't know enough about Butter to know if in her situation practice would bring up a coding score - I just wanted to note that some skills in some children really aren't able to be pulled up to the level considered "normal" and for some of those children, parents often find they need to make a choice, do we focus a huge amount of energy in a direction that is not going to lead very far, or do we put accommodations in place and give our child time to pursue areas of strength.
polarbear