You can make a decision that someone has a permanent right of residence under the five-year rule (DWP has now quite properly disowned the bulletin in which they said it is exclusively a Home Office decision).
In this case, the nature of the claimant’s incapacity is relevant. If she was temporarily incapable of work, she would retain her worker status after she went sick in 2005 and would have completed her five years some time in 2009. But if the incapacity were permanent she would appear to have failed to satisfy the prior residence requirement of two years. But that residence requirement is waived if the claimant was permanently incapacitated by an industrial disease or accident.
Got any more info on the nature and severity of the claimant’s condition?