Almost all 1891 census records for Ireland were destroyed.
In other parts of the UK it's possible that you GGM's name was spelled differently by the person who filled the original form out or transcribed wrongly by either the census enumerator (who copied the original forms into an 'enumeration book' for his/her district) or during the digital transcription.
If you haven't already done so, try using 'wildcards' and perhaps a wider age/location range.
You could post your GGM's name and DOB. Perhaps someone here can find her.
Mike