Please help!!

I've only just seen this. Roger Wilmut's book "Tony Hancock: Artiste" gives the complete cast lists - including extras - for every Hancock's Half Hour but Pamela Morgan is not mentioned.

The episode she was almost certainly in would be the "East Cheam Centenary" which is on Disc 6 of BBC's "The Tony Hancock Collection", the DVD collection of all the surviving HHH programmes.
This particular episode revolves around a parade to celebrate 100 years of East Cheam Borough Council which TH somehow came to be serving on.
There are various shenanigans played against each other by Council members hiring their property to the 2 TV channels at the time and Hancock manages to convince the BBC to pay him money to use his house at Railway Cuttings to broadcast the parade.
Anyway without issuing any spoilers Hancock parades past his own house followed by some people dressed in costume that include some familiar faces from the Hancock's Half Hour cast and they are followed by about 15-20 children, most very young just following the procession on tricycles and other various forms of children's transport toys and some just walking along.
I think this was one of the very few times that the show went outside of the studio and the only one I have seen which includes identifiable young children. The children obviously would not have been named in the cast so Pamela Morgan, like the other children wouldn't be mentioned on any cast list.
In this particular broadcast you get to see what the famous broadcaster John Snagg looks like as he goes into Hancock's Railway Cutting's abode to do a running commentary.
I don't know if you are still looking for an answer all these years on but this is your best bet if you are still looking.

Did you ever find that episode? YouTube has all kinds of them! Also one of the torrent sites has quite a few to download.