Jane, It is sad for me to relate to you that there are only two place in Dublin city now where your friend will be able to get fabrics - and neither of them is great! One is the Dublin Woolen Mills which is across the Halfpenny Bridge from Temple Bar. Upstairs they have a small collection of quilting fabrics with a larger section of haberdashery downstairs. The other is Hickeys which is in Henry Street, which is mainly unholstery and bridal fabric but in the basement they have a small collection of quilting fabrics. They are not cheap at all and the selection is very poor. The only other place in Dublin is Fabric Matters in Rathfarnham which is about 30 minutes from the centre but she would have to book an appointment as it is run from Wendy Huggins home.
http://www.fabricmatters.ie
Other places of interest: Trinity College - the grounds are lovely to walk around and the library houses the Book of Kells; Dublin Castle is right in the centre of town and worth a visit; behind it is the Chester Beatty Liberary which is really a museum and it's my all time favourite. It has a very pretty little garden at the front and it is so quiet you would never know you were in the city. It has a restaurant too. If she is interested in seeing what a Georgian redbrick Dublin house was like then Number 29 Fitzwilliam Street is open to the public. The Royal Hospital in Kilmainham which is a 17th Century building and houses the Irish Museum of Modern Art is also a lovely place to go and only a short taxi ride from the centre; The Casino in Marino is an 18th Century neo-classical building which is perfectly formed but on a tiny scale and again only a short taxi ride from the centre. The National Art Gallery in in Merrion Square is lovely too. Another favourite of mine is the War Memorial Gardens in Islandbridge where the gardens were designed by Sir Edward Lutyens. It is a memorial to all those Irish men who served in WWI. The gardens and the beautiful architecture have been renovated and it is now open to the public. We used to play around there when I was young and it was completely overgrown so I am particularly pleased that it is back to its former glory. There are two little houses that list the names of all those who served and died.
Dublin is a very small city so everything is within walking distance - but it depends on your health I guess. All museums etc., are on a small scale (not like the V&A or the Louvre) and most places have a coffee shop to rejuvenate the spirits!
I have included a few websites for these and various other places that might be of interest in Dublin. I hope your friend has a pleasant experience.
http://www.heritageireland.ie/en/
http://flyingbookclub.ie/
http://www.visitdublin.com/See_and_Do/Dublin_Top_10_in_2012