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(the following paragraphs are made on the assumption that the CoE-RoA were issued under the the same sections of the Immigration Act 1971, not the BNA 1981.)
This is, to an extent, irrelevant. The Immigration Act focuses on those born, naturalised or registered in the UK itself, not the former colonies.
Is she mentioned on the certificate herself? The sections of the law that you quote align more precisely with those of the Immigration Act 1971, rather than the BNA 1981 and I therefore suspect that your mother was registered herself as well.
Briefing: what is the ‘right of abode’ in UK immigration and nationality law?
For an Ancestry visa, it only applies if you have a grandparent who was born in the UK. This doesn't seem to be the case if your grandfather was born in India.
Unfortunately that doesn't count. The grandparent MUST have been born in the UK (England, Scotland, Wales or northern Ireland). Being born in British protected state is not the same.
Still doesn't qualify you for an ancestry visa. It has to be UK born grandparent and you have to have the evidence to prove it.
Worth exploring if this made a parent British otherwise than by descent under 14(2).
The question becomes: Was your mother British otherwise than by descent or British by descent?