I think that you should get onto the Irishgenealogy.ie website and see if you can find a death certificate for her amongst the civil records. Death certificates are available on the site for deaths occurring between 1845 (1864 for Catholics) and 1966. (By the way, the site is an Irish government site, and free to access.)
You are usually able to view and download the registry entry as part of an image of the whole page in the register, and it does include age at death - but be warned, whoever the informant was, they may not have actually known when she was born, so may be guessing, or passing on what she claimed to be her age.
I hope this helps,
All the Best