Assuming (very dangerous) that Margaret was the first wife of your George Edkin and, again, assuming that he was still in England when she died and was buried, then he left Lancashire after her burial date of March 1791.

But, as you say, it is more likely to be George's jnr's mother Margaret who died in March 1791 which means George snr didn't leave Lancashire until after March 1791
I am trying to fill in the baptism dates for George snr and Margaret as there are some large gaps and even a couple of the knowledgable trees online which I looked at, seem to have missed Jenny's baptism, and the burial of the first John.
Bapt 25 Mar 1764 St Mary, Lancaster, Lancashire
Jno. Edkin - Son of Geo. Edkin
Burial - burial 6 May 1767
Bapt 4 Feb 1776
John Edkin father Geo.Cockerham (two sons named John, see burial of previous 1767
Bapt 9 Mar 1767 St Mary,
George Edkin - Son of Geo. Edkin
Bapt 3 Dec 1769 St Mary, Lancaster,
Sarah Edkin - Daughter of Geo. Edkin
bapt 28 Feb 1773
Jenny Edkin father George Cockerham
There is a 10 year gap with no births
bapt Margaret 17 May 1781 Cockerham Lancs
bapt Francis (son) baptized 9 May 1784 Cockerham Lancs
Evidently there is a report of George's death in 1848 in the Muncy Luminary 4 Mar 1848. I wonder if that happens to mention when he arrived in the US. I have no idea about searching for US newspapers. Unfortunately the earlier US censuses don't say when the person immigrated and I am having absolutely no luck with shipping records.