Custody of my daughter in Delaware?

Me and my daughters father both have custody of her, and I'm planning on going to TX for a week to see a few of my friends before they leave for deployment for a year. And I will not be bring her with me. A 36 hour car ride with a 2 year old in my opinion isn't a good idea. I have asked my grandmother to watch her while I am gone she said yes; But my grandmother told me once I get back I will not be able to get my daughter from her. Last time I checked in the matter I have custody not her. Is my grandmother allowed to try and keep my daughter from me when I have custody? or is she trying to bullshit me into not going to TX.