If you think the Liverpool death looks promising, it might be worth investing in a copy of the death certificate. If, for example, the death was registered by a name you recognise then at least you would know it was the right Susannah Webb, as well as where she had been living and the date and cause of death. It's a bit of a gamble - not recognising any names on the certificate is likely to mean it's the wrong person, but not proof.