I live and work in BAH.
Mum will be able to see the whole country in 3 to 5 hours. All that is of any interest to the tourist at least. I am guessing the local shopping malls etc are of no interest.
The easiest thing for you / her to arrange would be the following.
Call "Bahrain Limousines" on +973 17-266 266 and arrange for a car and driver for a few hours. (Not expensive! Arrange for an hourly rate (should be around BD 6 to 8) and tell them you would like to do some sightseeing. All their drivers speak English quite well and their cars are in top shape.
The driver will meet Mum at the airport or hotel.
Gulf Air should provide her with a day-room (especially if she is paying a full-fare F or J class fare). Usually this will be the "Movenpick Hotel" (lovely, new, great food and just 300 meters from the airport) or the "Gulf Hotel" (also not bad, but closer to town).
A 24-hour transit visa is issued without any fuss at the airport and may cost BD 3 to 5.I say "may" as sometimes GF pays for this.
Sights to see are -in no particular order- "Bahrain Fort" in Seef (near all the shopping malls, "Riffa Fort" -aka Shaik Salman bin Ahmed Al Fateh Fort- in Riffa (lovely, very Lawrance of Arabia), Al Jazzra Handicraft Center (where traditional arts and crafts are demonstrated) and the nearby Al Jazzra House (where the current King was born) bothe very, very close to the causeway/border to Saudi Arabia. (you can drive half way over the bridge (small toll) to the little island where the border crossing is, have your picture taken and come back to BAH).
Arad Fort, only 1 or 2 kms from the airport can also be of passing interest.
The Grand Mosque is also open to visitiors and the folks there are very kind and conduct guided tours on an on-demand base. (they will provide "suitble coverings for the ladies" and give you a free copy of the Holy Quoran in your choice of language.
The Bahrain National Museum is also interesting and cheap as chips to get into. If it is a hot (or rainy) day, it can pass an hour or 2.
The Manma Souqu (bazaar) in town at "Bab Al BAhrain" (gate of bahrain) is OK, but do not expect anything like in Cairo or Istambul. And you might want to go there with your driver. Otherwise you might get lost.
Then there is the Bahrain International Circuit where the F1 races are held and the nearby Al reen wildlike park - a bit basic, but quite cute. Definately not a priority, unless you want to see a camel.
And then of course there is the NUMBER ONE "attraction" of Bahrain, THE TREE OF LIFE, out in the desert (or shall I say gravel fields and scrap yards) near Riffa (combine with Riffa Fort, if you go). It is, well, a tree. That's it. It stands quite alone in the barren landscape, is vandalized and graffity-ed all over and usually surrounded by quite a bit of garbage. I think Bahraini boys take their dates out here to go "parking", ifyou get my drift...
Over all, a few hours should be fine for Mum. And tell her to get some rest, before the 17 1/2 hour flight to Sydney. (She can get off the plane in Singapore for about 1/2 hour the stretch her legs and buy some decent coffee...
The people here are friendly and it is a safe place. Nothing to worry about (unles George Bush decides to invade Irak, in which case we will have some trouble here....
)