Expression of Wishes Advice

The Pension company were supposed to have written to my partners sister asking her if she wished to make a claim on the fund; however, they failed to write to her despite insisting that they had (which they now freely admit some 9 months later and have now supposedly written to her and I now have to wait another sixty days for a decision); - infact, they later sent the forms to me to pass on to his sister (truly) which I could have easily filled in and returned stating she did not wish to claim !!! (what a sham).
All I am concerned about is ensuring his sister does not get a cent as my partner truly did not want his sister getting her hands on anything, hence why he wrote a Will leaving his entire estate to me and also a codicil stating why he hadn't included anyone else in his will. The reason I want to see the EOW is I know his sister was never named as a beneficiary.

yes, my partner and I legally lived together for 18 years, had a joint and individual bank accounts, bills in each others names, shared credit cards etc.