Ok, I think it is this teacher's interpretation that the mark comes down a lot due to spelling.
Do you get to see your child's literacy work regularly? If so, you should work on spellings she gets wrong regularly.
Work on grammatical rules connected with spellings at the same time e.g. Forming plurals, forming the past tense of a verb.
Work on words with letter patterns in common together e.g. Wh in where, what, who, whine, wheel etc but w without h more common - look in dictionary to see this is the case; a after w generally makes /o/ sound e.g was, watch, want, wallaby, wasp, what, At after w generally says or e.g. Wart, warp, war, warthog,warble
Make her an alphabetical list of first 300 highest frequency words and encourage her to look up any she thinks she might have got wrong. Ther are several techniques a school could use to cultivate good spelling during school. Some schools do not. Find out what your schools are and connect with them. Try an ace spelling dictionary.