Our presumed Millie's father Frank / Francis had a brother George Plank who was living in Foundry place 1891. He was is a few doors the Newbridge Arms, following on from Bridge street - where the famous Ponty bridge is). In 1901 he's married with a daughter Florance at Bonvislton Rd, Trallwn. In 1911 they are at 78 Tram Rd (street was later re-named and is now as The Broadway Pontypridd).
There were 2 Carhart families in Mountain Ash, but the one was from Cornwall. Milly was in the same school register as one of the daughters, but G W Carhart not named in that register.
Could Milly have met W G Carhart at a Church event ?
One of G W Carhart's brothers who also went to War desCribes his religion as being Plymouth Bretheren, so not sure if the Carhart's listed in the newspaper are the "other" family. However the Carharts are living in St Illttyd's cottage in 1911 and this is described in one newspaper article as Church Cottage.
The Carharts seem to have mainly stayed in Mountain Ash I think one or 2 of the daughters married and then moved away.
Frank Plank also dies at 45 Miskin st in 1945.
So the nearest person to Pentyrch geographically was George Plank.
Presumably you are in possession of some sort of handwritten original of the poem ? Or is it a newspaper cutting ?? Could someone have just liked the poem and kept a copy of it?
In case you haven't seen it, there is a portrait photo of GW Carhart in a 1916 newspaper wearing his Seaforth Highlanders Cap.