M J Goldsmith was Mary Jane Goldsmith. In my book, I explained that two Gosling sisters - Mary Jane (known as Jane) and Esther Annie (known as Annie) - both worked as domestic servants for the Barries in their London home. Jane was the first to be employed, and Annie was taken on later. Jane left when she married Edward Goldsmith in 1898, and Annie left later (I think when she married Thomas Archer).
I should be very interested indeed to see the letters you mention, and hope that I might help decipher them for you and, hopefully, for the benefit of Andrew's database. My grandmother worked for the Barries at Black Lake Cottage from 1903 to 1909 but, to date, and to my great disappointment, I have discovered no correspondence between them.