Readers' forum: Cross-border tax

My client was born in the Irish Republic and her parents are Irish too. About 15 years ago she married and moved permanently to Northern Ireland. She continued to work in the republic from Monday to Friday travelling to and from work daily.

Her only source of income is the employment income from the republic and investment income. Some of the latter is paid gross and some net and both are a mixture of UK and Irish sources.

Given that she is resident and ordinarily resident in both countries and domiciled in the republic in which country should she be assessed to tax? Under the double taxation agreement I believe it is the UK but I am now confused.

Can readers please advise what should be declared on an Irish tax return? Also can they advise on the relevant pay-related social insurance (PRSI) and universal social charge...