Kate Pink

I am trying to find Kate Pink youngest daughter of Benjamin Pink and Agnes Williams she was born 1867 at 9 King Street, Camden Town, England. After Agnes died, Benjamin came to Australia with his two oldest children leaving Kate with her maternal grandparents Thomas and Mary (Martin) Williams in Herdford. I have traced her to the 1891 census but since then have not been able to find her. I have bought 3 marriage certificates for Kate Pink that thought were going to be the ring ones but of course they wern't . Any suggestions of where to go now.

Thank you
Gwenda
Australia