It's funny but I was thinking about this a couple of months back in a somewhat different context. I had come across a high school student advising a younger student who was complaining that but for his many silly mistakes he would have made honor roll on the AMC10. The advising student pointed out that many of his "silly mistakes" were likely due to his lack of true mastery of the mathematical concepts as well as lack of facility with solving complex problems. He pointed out that he himself rarely make silly mistakes on the AMC10 and AMC12, but that he used to make lots of them a couple of years back when he was merely familiar with these same concepts and relatively inexperienced in solving complex problems. Anyhow, I think he is correct. If it is taking too much of your brain power to understand and solve the problem, it is much easier to make one simple calculation error among the many required calculations.
I don't think that it is computational practice that your DD needs unless she has not already mastered her math facts. Obviously, fast and accurate recall of math facts may help reduce computational errors; however, I think that she has to develop a deeper understanding of new math concepts as well as automate certain procedural steps. For example, the ability to glance at an answer and see that it doesn't make sense in the case of decimals or automate Divide-Multiply-Subtract-Bring Down (Daddy-Mommy-Sister-Brother) so she doesn't even have to consciously think it anymore.
