Totally agree with children helping each other, learning to be compassionate, etc. But the school needs to step up and do its job. Organise things so the school pays the price, not another child.
WHY should any child miss lessons? If her parents took her out of school for that many hours, they'd probably be fined. Double standards, anyone?
WHY choose a compliant middle-set child? As Op asked, why not choose a child from the top set? Who presumably is better able to catch up on the missed classwork.
WHY should this child's own friendships be threatened by the school's inability to help another student? If op's DD is forced to spend 4 break periods out of 5 with the other child, how long until her best friend finds a new friendship? It's a fickle, often insecure age.
WHY was the poor boy moved to a different class because the school can't manage his TA? How does this TA get off telling a child their book is babyish (whether or not she understands dyslexia) or contradicting the teacher's instructions to help the boy with maths??
WHY don't they adjust a teacher's schedule to run lunchtime sessions - thaose don't interfere with lessons or breaks - like the example above, which was so well handled that other children asked to join.
Obvioualy schools need to juggle so every child gets a chance - but the juggling should come from the school, not at the expense of other children.
Op, obviously you don't want to go in all guns blazing, but I'm fuming on your behalf. I suspect DD and friend are accurate about what the TA told her - I'm only hoping the TA was wrong, as she doesn't sound very competent. Good luck on Tuesday!