Welcome (from the UK, though I'm in Scotland where quite a lot is different). As everyone says, yes it's common for bright children to make mistakes on simple things. I did want to comment, though, that I think the right response depends a bit on what it is. When a child who can do multi-digit multiplication is being given page after page of single-digit addition and gets some wrong, it's reasonable to ignore the silly mistakes because the task was inappropriate. But if a child is being given a writing task which, overall, is at the right level, but is making basic mistakes while not making more "advanced" mistakes, that's a rather different situation. My experience is that (unlike much else) writing assignments for this age group are largely self-differentiating: e.g., asked to write a story about a castle, an advanced child might use more complex language, have more interesting characters, etc. - the task itself would be appropriate for any age (even if the expectations of what would be produced were off). Is it in that kind of situation that your DD is making these basic errors? Or are they only or mostly showing up only in situations where the task really is inappropriate, e.g. some very tedious comprehension exercise?
If it's the first, then the errors seem less analogous to the mistakes on pages of single-digit arithmetic. It's more as though the child was getting wrong answers to the multi-digit multiplication because of errors in the single-digit addition that has to be done as part of the multiplication. After all, there isn't an advanced level of writing at which it no longer matters whether you capitalise correctly or can spell simple words. (Well, maybe once you're writing with a word processor that can correct you...) In this case I might have a chat with her and point out explicitly that the simple things are still important even after you learn to do harder things.
Or maybe this is a sign of a general lack of engagement with school, due to boredom, so that even when she does get a task that would be suitable she still rushes through it? What does she say she thinks of school work? What do you think of the school and her teacher? What kind of record do they have of differentiating effectively?
