It’s possible to have both, but it would be very unusual for your child to need both.
Here’s why: Everything that’s in a 504 plan can be included in an Individualized Education Program (IEP). The IEP can also provide services and supports that would be not available in a 504 plan. So if your child qualifies for an IEP, typically there is no reason to also have a 504 plan.
One instance in which a school might want to create a separate 504 plan is if a student who has an IEP breaks her hand. She might need some accommodations for a few weeks because she can’t write while her hand is in a cast. If so, the school might decide to put those temporary accommodations in a 504 plan rather than adding them to the IEP.
But typically a child would not have two plans. Frankly, you wouldn’t want both. It can take a lot of time and energy to manage even just one plan.
The big question is this: Does your child meet the eligibility requirements for an IEP? If she does, then everything she needs can be covered by the IEP.