Hold Right of Abode, Need UK Citizenship

[Serengeti]

My mother is a commonwealth Citizen, and holds a UK Right of Abode. She claimed as "A female Commonwealth citizen who is, or has been, married to a man with right of abode at any time before 31 Dec 1982 2(2) 2(1)(b)" - she was born outside the UK in the Commonwealth, and married my father in London in 1975. She has since marrying my father held the right of abode, although he passed away last year.

The ROA process is now very cumbersome and expensive, and we are looking to convert her to UK citizenship to avoid the hassle that she has to go through every 5 years to transfer the sticker from passport to passport. The gov.uk website is not clear on whether she is eligible to apply for UK citizenship by virture of her current status as ROA-holder. It is clear on what happens for ILR -holders, but not ROA -holders. She lives in the UK, but spends a lot of time in her home country so will not meet the 90-day per year limit for time spent outside the country if applying to naturalise via the residency route.

Any advice is much appreciated.