Women Glide swing - full extension?

[Jumpingbunny]

My daughter’s bar routine starts with two glide swings (the gymnast regrips between glides). I’m confused about how a glide shows “full extension”. My daughter is short enough that she could fully extend with a straight body but her coach makes her hold her body in a dish shape (pic attached). It’s harder on the abs and harder to show full extension. Anyone have any thoughts here? My daughter would rather do it in a straight line without the dish shape.