Hi there,
have sent that e-mail so fingers crossed she will get to you on here. By the way it was De not Du Pont!
Spidermonkey - maybe there is more subterfuge than meets the eye here! Good one with marriage, the Damois marriage was at St James Moss Side 1893 so would be the right time frame. Maybe it is a transcription error.
There is a Hotense de pont on London 1891 duaghter of Alexander and Angelina nee poss (love it when the in-laws are over!

aged 8 and then in 1901 there is a 29 year old Hortense de pont in Urmstom. Her father was a merchant born Switzerland but she is working in 1901 as brushmaker, born London. So either de pont is wrong or Edith l was illegimate.
Do let us know how you get on.