I will see if I can help you. Leady would also be spelled as Leddy, Liddy, Liddi etc. so keep an open mind on spelling as often it was written down by someone else ie. the census taker, the registrar etc. You are very fortunate to have your family on 1821 Census as it is a rare document to have survived. Utilise all the resources on https://genealogy.nationalarchives.ie, focus on wills etc. to see if any of them are mentioned As civil registration did not start until 1864 for catholics, do not overlook it as you would be hoping that some of the younger members of the family lived for another 43 years and that their death was registered, look at who was present when they died again hoping that it was a brother, sister or any other such relative that would help you make the link. You have not told me what Ellen's married name was.
You can also take out a short term subscription on Roots Ireland, it covers the baptismal, marriage and some death records. Do look and see if the records are available for your parish. Look for grave listings on line, volunteers are recording and putting them up all the time, women often buried with their family as opposed to their husband, particularly if they died before their husband, perhaps to allow the husband move on and remarry. You could engage with Cavan Genealogy for a fee they can do research for you at Genealogy Centre Contact Details
1st Floor, Johnston Central Library, Farnham St., Cavan
Tel: +353 (0) 49 4361094
I don't live near the area you mention, so I am not too familiar with it, however I hope I have given you some new lines to search and please accept my apololigies if you have done all of the above.