I might also add, it may be worthwhile contacting the Housing Section of the local authority (County Council) in the area in which she intends to live. They can best advise in terms of housing options for older people.
If this lady has worked in the US, it is possible to transfer social insurance contributions from the US to Ireland (we have a bilateral social security agreement with them) so this may help her qualify for a pension here. Staff in your local social welfare office can advise - but I would suggest checking this in advance of returning to Ireland.
If she is in receipt of a pension from the US, it is also likely she may qualify for the . In addition, depending on her income, she may also qualify for a medical card or a GP Visit card. She will automatically qualify for a medical card once she reaches 70 years.
I might also suggest taking a look through the [broken link removed]. It explains the taxation system in Ireland and how income from abroad is treated for tax purposes here (among other items).
The age of this individual should not really be an impediment to her seeking employment here in Ireland if she so chooses - depending on the nature of the employment and the employer, of course. I would imagine however if she wishes she could obtain some work as a Home Help or a Carer - given her nursing qualifications she should have no problems.
It's also worth noting, there are issues regarding entitlement to health services in Ireland - but given she intends to return to Ireland and remain living here for at least a year or so, she should qualify for public health services on the same basis as everyone else.
I hope this has been of assistance.