Maura,
Yes you can effect a PRSA, but if you have no income than you cannot claim tax relief. And if you cannot claim tax relief it makes no sense, as you will be taxed on any income you ultimately draw down at retirement.
If you cannot get tax relief you would be better off investing into a non-pension savings type product where you will only pay 23% exit tax on the growth.
After taking the 25% tax-free lump sum , the balance must be used to buy an annuity of invested in an ARF. Any income coming out of such will be taxed at appropriate rate.
Therefore if she is not getting tax-relief on contributions it is pointless investing in a contract where she will pay tax on income (original contributions + growth) as opposed to investing in a contract where she will only pat tax (exit tax) on growth.
Finally tax relief is only available on contributions coming from earned income. I dont think that maintenance payments count.