Yep...she's too bulky to manage flying up to a roost. You might fix her up a roost she can manage like a hay bale or similar soft spot that is broad and not too high. Sleeping on a hard surface can start putting pressure areas on her breast and cause damage there. If your nest boxes are high...
Tell that to the many here on BYC that are eating eggs laid by meaty hens. Aoxa would be mighty surprised to find she should have processed those hens she bred to her Barred Rock male and is currently raising their offspring. I've known of people getting their CX hens to the age of 3 before...
That's not a White Rock, that's a Cornish White Rock Cross hen...a meat bird. More commonly written as "CX". Has WR genes back in her breeding but most decidedly NOT a WR.