iInoticed that this question was posted four months ago, so your school may have already addresed your concern. However, your post has a few ideas which require clarification:
1. How do you define "well below her grade level"? NJ doesn't begin state testing until third grade so your comparative sample is localized to your daughter's current and previous classes. Judged against her immediate peers she may be underperforming, against the rest of the state she may be doing well.
2. Define "most subjects". Which classes does she perform poorly in?
3. How much time does she spend working at home? Typically, HW is limited to 10 minutes per night multiplied by the grade. Follow that rule beginning in the third grade (3rd graders shoud be doing about 30 minutes per night, 4th 40 minutes....). Before third grade some work should be done at home so the student understands that taking work home is the norm and not the exception in order to be successful in the classroom.
A previous comment mentioned RTI ,and as cumbersome of a process it is, it is unfortunately the national norm. The premise behind RTI is this: 80% of a school's population will do fine in its general curriculum; 15% or so may require some form of intervention to succeed (pull out reading or math programs, a researched based and proven computer based program, etc.), and the remaining 5% will require the most intensive form of intervention which is an i.e.p. or special education placement.
RTI is designed for EARLY prevention which is exactly where you are now so you have every right to push this issue. Discuss her strengths and weaknesses with her teacher about a month into school. This should give the teacher enough info about your girl for her to detect what gaps, if any, are there. Her school should also start baseline/diagnostic testing during her third grade year. Most schools refer to this as MAP (Measures of Academic Progress) Testing. This diagnostic tool, while not an exam, will gauge where your daughter lies within her peer group. Based on this info, your daughter may be referred to her school's "core team" who will then devise an intervention plan if needed.
The process used to be much more cut and dry and involved discepancies between IQ scores and classroom achievement. While cut and dry, it failed to control for something that schools hate to talk about: poor teaching.