Oci for Widow

Hi quick question of anyone can help me here.

I am applying for my mum's oci. She was indian citizen previously now british citizen. She is applying for oci within herself roots to India. She is a widow. I am little confused does she need to provided marriage certiricate still? Also the application still asked for my dad's detail although she is widow. Can someone please explain what other documents need to be provided apart from regular mandatory documents. Thanks.