I learned in grad school that English spelling is mostly a matter of memorization. This is because so much of English pronunciation doesn't follow phonetic rules (i.e. though, through, tough, cough, dough, etc.). The easiest and most painless way to help a child learn to spell is to have them read, read and read some more. Reading the same words over and over again (in literature particularly, not necessarily in drills) will help imprint them to memory.
I really want to emphasize that your child shouldn't worry about spelling while she is writing. It is very important for ideas to flow out onto the paper in a smooth manner. Stress can kill both memory and creativity! Spelling and grammar should be edited after the writing, homework, worksheet, etc. is through!
If you think your dd is already stressing out about spelling while she writes, here is a fun activity you might want to do with her. Have her dictate stories to you while you type them up (and spell check them for her too!). That way tripping over the spelling does not stifle her creative juices. Afterwards, she can read her own story with all the spelling correct, and illustrate it too. Children often find this very rewarding, and it is another chance to see words spelled correctly and help that memory!
Interestingly, teachers often have terrible spelling skills because they have seen words spelled wrong so many times they can no longer differentiate correct from incorrect spellings.
DaryLLL, using to and too incorrectly is a huge pet peeve of mine too. :LOL Same with there, their, and they're!