motiztab,
As pabone stated above, seat height is the same on the Bonneville regardless of whether it's a T100 or a standard model. The seat height listed for those models is 775mm.
Per past and present Triumph specs listed on Hermys website, I find listed a seat height of 720mm for an America and Speedmaster; a seat height of 725mm for a 2000 Legend and Adventurer; and a seat height of 675mm for a 1999 Legend and Adventurer.
Looks like a 1999 model Legend or Adventurer might be your best bet for the little lady. I don't know if or when those models were ever sold in the UK, but here's a link to the specs I pulled from...
Hermys.com