Why don't you order the birth certificate of one of her children - this will be one of your grandparents as it will be recorded on this. If your grandparent was born after a certain year (sorry - can't remember which one) then in the births register it will have their mothers maiden name in the register. That's how I knew that the birth of a baby in 1916 was related to me as I could see the mothers maiden name in the register, so I knew I was ordering the correct certificate. If you order the birth certificate from the registry office where the birth was registered then it will cost you �7.
If you have any other questions on your family history you may be better posting them in the genealogy section under the history heading.
Good luck.