See if P&O Arcadia have an iterniery you fancy in 2008, very nice ship, excellent sericer and no children as its adult only.
I highly recommened celebrity relaxed , elegant but yet fun.
Try Fred.Olsen also. They offer mostly 'no-fly' cruises which your mum may prefer. They're a traditional cruiseline that cater for the over 50's best & their prices are very reasonable too.
My bet is fred olsen. Most other ships are too big and confusing. They are really a very good line especially the black watc.
I would suggest the QE2, your mum will love it - also, if she likes to dance, the QE2 has dance partners always available for the single lady or gent. This is something that is not offered much these days but is expected on the QE2. The ship is a little out-of-date these days compared to the modern superliners but that is to the good as Cunard now offer cruises on her at very silly low prices these days. The QE2 is still the most famous ship in the world and thought to be the finest by those that have never been on her. In certain respects she is still the finest and in every port she visits she is given respect by all the other ships she meets. A few years ago we were lucky enough to cruise a sector of her Round-the-World cruise and we were saluted when we arrived in the ports and played out by a band when we departed - the passengers lined the rails and waived goodbye and for those few minutes each time we felt like royalty!! Next year the QE2 will be sailing around the mediterranean from May through to October - always out of Southanpton and returning to Southampton - thus no need to fly, which is a real bonus! Plus you can pack whatever you like and take your own car to the port.
Forget the rest - go with Cunard who are still the best, even though Carnival are her new masters.
Just back from a cruise on the QE2 with my Mother-in-law and it was excellent for her & I would highly suggest this ship.