Dawn...You say there were 3 Ada Fanny Wrightons born in that time period...I found only 2...Ada Wrighton born Mar Q 1881 and Registered in Brackley, N'hants...and Ada Fanny Wrighton registered Sep Q 1882 in Brackley, N'Hants...and then this one born in 1870
here's the problem I see...The Ada born in 1881 to Henry and Julia was not with her parents in 1891 and she was not in service..because she died in June Q 1881
Ada Wrighton b abt 1881 died Apr-May-Jun 1881BrackleyNorthamptonshire
I find nothing for another Ada born 1883 in N'hants..I did find one in Huntingdonshire...so the only thing possible is that the Ada Wrighton born 1883 that Bill Watson found for you was your Ada..not Henry and Julia's Ada...like you previously thought...Maybe ...and I am not dispelling any of your family history...Maybe when your Ada said she went into service at 11 years old..and worked for the Fortescue family till she married...she may have meant " I went into service at 11...and then I worked for Fortescues until I married"
Hope this helps you somewhat...