There is nothing in Section 604 TCA 97 to explicitly extend the relief - it would come down to an argument about whether or not the house continued to be the individual's PPR while they were in the nursing home, which is something that would rest on the facts of the case.
If there is no valid expectation that the individual will ever return to occupy the house again, or if they had gone to live in the nursing home (or more likely a retirement village) purely because they wanted to, then it would argue against the house being their PPR.
If their belongings have been packed up and the house let to tenants, then that would strongly argue against the house continuing to be their PPR.
If on the other hand, the house has been left as it was, awaiting the owner's return, then one could argue that the time in the nursing home is no different, in fact, than an extended stay in hospital.
It would be an interesting case, if it were to be argued, but I'd say the likelihood is that an Inspector would be unlikely to restrict the relief in such circumstances, but I've never actually heard of it arising as an issue.