Understand how long term visit visas work.
The applicant (your mother) needs to show a track record of multiple standard visit visas and that she returned home within the time she mentioned on the application form. There have been a
case recently when people who have overstayed what they stated on their application forms (so, for instance, if they said that they were visiting for 6 weeks and stayed 6 months) were refused subsequent visit visas.
Once your mother has a track record of multiple visit visas, she could apply for a two year visit visa. But even then, that merely means that she can enter the UK for multiple times, but for a maximum of six months at a time. She is also expected to spend more time in her home country than in the UK. UK visit visa rules expressly forbid
residing in the UK under the guise of a visit visa by frequent and successive visits. If there are such repeat and frequent visits, the long term visa can be cancelled on the spot at the airport and your mother returned to India by the next available flight. Any subsequent visit visa application will almost certainly be rejected.
Remember that you becoming a British citizen does not give your mother a pathway to UK immigration.
Do you have a family? You may want to look at the Surinder Singh route, which will involve you moving yourself and any family you have in the UK to another EEA country, exercise treaty rights there, prove the dependency of your mother on you, get her to join you in that EEA country and then move back to the UK. This route is under EU law and time is running out for it with Brexit.
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.