I would second Star and want to know how much training the staff have had and when, not if, the school is planning a staff training day on SEN and inclusion - particularly hidden disabilities. There is no excuse for 'forgetting' they have her statement and know she has additional support and extra sessions.
My ds had similar issues with homework, particularly tests. He has a slow processing speed and in primary was in top set for everything, as he could demonstrate his level of understanding, but still failed all the timed tests.
I spoke to the school and inclusion team and explained that by not differentiating in some way for all these tests (and there were a lot) they were actually discriminating against ds and setting him up to fail, which was having a really negative knock on effect on his self-esteem and confidence.
The school suggested he could be given extra time for tests, but as they are always done at the end of lessons, this meant he would lose some playtime on each test day - again discrimination and not a solution he would have gone for.
In the end I got them to agree to work out ds's results against the number of questions he'd answered, rather than the total number of questions asked.
In lessons where he wouldn't lose playtime if he continued the test after the others, he drew a line under the question he was on when time was up and then finished the other questions.
When we were finalising his statement I made sure it included extra time for all tests and assessments, not just official exams, as otherwise his predicted results were always underestimated. The school SENCO tried to tell me he would have to be tested by her before every test/assessment/exam to ascertain whether he was entitled to extra time - that was rubbish, he's entitled to extra time just by virtue of having a statement and so is your dd. On top of that, in ds's case the EP had included his processing issues in his statement and said that he should be allowed extra time for all tests, exams and assessments - which double underlined his right.
The school gave him the extra time, but moved him down a set for maths in y7, as they wanted to hothouse the rest of the group through level 6's. 
He gave up and didn't bother trying in maths for the rest of the year - end result was that he got a 5c. If he'd been kept in the top group I'm pretty sure he'd have got a 5a, but I was more angry about the damage to his self-esteem than his test results.
He is now in an indie ms secondary - funded by the LA - this school is all about individual targets and working with individual's strengths rather than focussing on their weaknesses and as a result he gained two levels in maths in the first term and reached the level he should have been at for his SATs with very little effort.