I don't think Marian McKenzie frequented the Cellar much, although definitely Hampstead where shw was resident. There was another regular singer of the 4 Mary's at both clubs, probably in the NW3 days before Marian, who had a guitar playing partner but can't quite place either of their names at present. She also was well known for Donal Og.
The old grey matter is failing on names however.
She would certainly have been on speaking terms with Roger as her partner was IIRC one of the Tuesday guitar crowd at CSH.