I'm concerned that you say you have told the school that she is having absent seizures, yet they don't seem to care. How have you informed the school? What process have you undergone? Have you presented an official diagnosis and physician's letter to the school that states that your daughter must have a 504 plan, and precisely what accommodations she must have in place? Have you met with the special needs department at her school to discuss a 504 plan? It may seem that they don't care, and they may not care in the way we wish they would or in the way we do as mothers, but they must comply with a doctor's orders.
An IEP is basically a difference in the way the curriculum is presented, for students who are unable to comprehend or master the regular curriculum. This is primarily intended for students whose intellectual disabilities limit their ability to follow the standard curriculum.
A 504 plan is an accommodation that the school makes, so that a student's special needs are addressed. Examples are: providing the standard material in a larger font for a visually impaired student, allowing a diabetic student frequent and unscheduled breaks to check his blood sugar or to get snacks, allowing a student with an anxiety disorder to take tests in a private setting or time to calm down in the event of an anxiety attack without being called tardy. It would seem that your daughter's absent seizures would not prevent her from learning, but would make it difficult, for example, for her to take a test in a timely manner. Perhaps if the rest of the class took a test that required 30 minutes, your daughter's 504 plan would say that she could complete the test with no time limits, or instead of 30 minutes, she could have 90 minutes.
With some children who have medical illnesses, the regular and traditional progression of completing a semester or a year of school just doesn't fit.
It's not about "holding them back". It's about allowing them to progress on their own terms. A student who has to have major surgery, for example, may miss most of a semester. Then the following semester, he or she may take a reduced number of courses at the hospital or at home. Yes, at the end of the year, he or she may not have completed fifth grade or eleventh grade like the other students, but the 504 plan will have addressed this, and either the student's course load will have been reduced, or else the student will be allowed extra time to complete that school year's work.
My own daughter took 7 years to complete high school, a task normally completed in 4. She was not held back, she did not fail courses. But she only took a limited number of courses due to her medical problems, and she skipped one term entirely due to the treatment she needed and due to her illness. She just didn't attend school that term, but she wasn't considered a drop-out, or absent, her schooling was just put on hold for a couple of months while she dealt with her situation.
So your daughter might not be held back, but her academic progression might look different from most kids' traditional academic schedule.
Be sure to have documented medical records, have your suggestions clearly written down (you know how much your daughter can do and how the seizures affect her), and have a meeting with the 504 team. Get clear recommendations from her doctor about what he or she thinks would be the best school setting for your daughter IN WRITING. Does she need more time to complete assignments? Should some assignments be shortened? Does she need to take fewer classes at a time? Does she need to rest or eat something or drink water after a seizure? Ask her doctors about these questions and discuss it with them, then with the school. My daughter's primary doctor wrote a letter to the school, informing them that he was actively treating her, and he outlined what accommodations she would need in order to succeed at school. It changed from time to time. One term, her doctor ordered her to stay at home and receive home tutoring from the school district. Another term he said she could attend but with certain stipulations. The process can change depending on your daughter's health.
The school system can require certain things, like physician's written orders, medical documentation, and a written 504 plan with which all teachers and staff must comply. You must meet with the 504 team at least annually if not more often, and keep them informed of your daughter's medical issues. And you must advocate for her, and help her advocate for herself.