You wrote: "She said he has always done this.
How long is "always?" (There's a difference between "He's been doing this for 2 years," versus "He's been doing this for 2 days.")
Does he have any hiding places? If not, maybe he's trying to use the gravel as cover.
What type of food does she feed him? If it's something that sinks, he may be digging in the gravel.
And.... well, lots of other questions come to mind!
More information is needed to really determine if there's an issue, or whether this is normal behavior. (I have a fish who sleeps completely upside down, in the middle of the tank. It doesn't seem to bother him, so I stopped freaking out after awhile!)
Can you talk to her, and if she thinks there is an issue, ask her fill out this form