For the most part, an aneurysm is a balloon like bulge in a blood vessel/artery. If the bulge keeps on growing, it can eventually burst, causing hemorage, meaning the blood leaks outside of the artery/blood vessel. It's like pinching a hosepipe, where if the hosepipe is soft enough, it forms a bulge which would eventually burst. Anuerysms is also not confined to the head but can form any where in the body where an artery is un-able to support the pressure of the blood flowing through it.
There is many factors that could cause an anuerysm...
Trauma:
Like in Fairy Godmother's case, trauma such as an accident, falling down a flight of stairs or any event that would cause the flow of blood in the artery to be disrupted.
Genetic Predisposition:
I have a genetic disorder, which for many reasons, such as heart-valve prolapse and weak arteries, make me highly susceptable to Anuerysms.
Cholesterol:
Cholesterol is the build up of fat in the arteries which causes an increase of pressure due to blockage... Like for instance if a rock or mud got lodged in a hosepipe.
Old Age:
The weakening of the arteries as a consequence of the aging process.
The biggest factors in determining the risk, is blood-pressure, relative age, cholesterol and the general health of your arteries.
If you are concerned, you can have your blood pressure and cholesterol checked by your local doctor. I am sure he/she will understand and try to determine wether there is any genetic predisposition in your family.
Were you told what the cause was of your Mom's anuerysm?
All of the best! Let me know if you need any further information