Does she have a vision impairment?

You need to email the special ed coordinator at your new school to start this process formally. If she has a 504 from the previous school, share that with them. It's not automatic!

Did she have a 504 in New York? Did she get/need extended time for regular tests?

You have to have a qualifying disability in order to get a 504, and that starts with an evaluation. Does your child have a disability? There is no letter from a doctor that will automatically grant a 504 plan. The process can take quite some time, so if your child has a disability you need to request an evaluation from the school.

What disability does she have? Does it impede her processing speed?

Start from there.

If no disability or learning difference, just have her take the exam under regular timing conditions.

I recently moved to DC from NYC where all students receive unlimited time on state examinations. I am trying to get a 504 for my daughter for the upcoming state examination specifically for the extended time accommodation. What do I need to submit to her school from a medical doctor? Is that accommodation difficult to obtain?