It depends on the breed - two years of solid egg laying is 'old' for a Hyline or an Isa Brown. The fact your hen has been laying non stop as those breeds were bred to do - puts her into the high risk category for EYP.
Check out her abdomen. Is it swollen? Do you feel an unusual mass in that area? If there is no sign of an offending egg, and that coupled with her history (age and dodgy egg laying) I'd be suspicious of egg yolk peritonitis. This condition requires antibiotics at best. Vet intervention or...