Inheritance

My aunt inherited slightly over the class b threshold from a relative. Confirmation of the inheritance and its payment took a long time (there was a suggestion that others might appeal the grant of probate but this didn't happen). Payment was made a couple of years later but in the meantime she had had a medical episode that left her cognitively impaired for a while (still recovering). She asked me for help with the transfer and I don't think she was aware that CAT liability relates to the date of death/probate as opposed to payment (I wasn't aware of this myself either). I only noticed this when I went to fill in the revenue declaration. What can be done at this stage as regards penalties etc? We are in Ireland.