Hi gdiphil, good on your mother - shame about your inheritance though!! OK - I have lived in Bahrain, what can your Mum do for 12 hours? They do have tours but she would probably be better to arrange that through her Travel Agent before she leaves the UK (I presume it's the UK) - I have never seen tourist buses like they have in London for example. They have a large Mosque that they do guided tours through. Ummm there are a couple of shopping malls. There is the Bahrain Souk - but probably not somewhere for her to go on her own and they are likely to be closed between 1/2pm to 4pm. Not being much help but there really isn't a lot to see. On a UK passport she should just be able to go through immigration with no visa needed.
My best suggestion would be for her to get a Hotel room - get a taxi driver to take her on a bit of a tour on the way there (and rip her off with the price) and get her feet up for a bit - it's a big trip for a 76 year old - even if she is flying in Business Class!
Hope this is of some use to you.