The 1891 Newcastle on Tyne, Byker, census has a Kathleen Curran aged 3 born All Saints Newcastle, with her father John Curran aged 31 Broker and Coal Dealer, b.Byker, Newcastle, and mother Elizabeth 30 b.Carlow Ireland. If you can't find her marriage it will be difficult to know which was the correct Kathleen.

One possibility is that she had a brief first marriage (husband died) and was therefore married a second time under a different surname. What dates were her children born? Have you bought all their birth certs, to compare the details given?

Sue