My mum is 88 years old and requires full-time carer as she

My mum is 88 years old and requires full-time carer as she suffers from a cortico Basel degeneration condition. She would like her niece 22 who is a Jamaican citizen to look after her in the UK - is this legal?
JA: What steps has your mother taken? Has she filed any paperwork with the UK government? What country does your mother live in? If different, what is her citizenship?
Customer: My mum lives in the UK from the 1960s. We have not filled in any forms. The first step would that she would come for a 90 day holiday and see if it works OK. If they wanted to make it permanent as a carer, we do not know the official steps and if it is actually possible or a non-starter
JA: Have you talked to a lawyer about this?
Customer: Initially my mentioned to solicitor and they said first steps is that she comes for 90 days and then take it from there
JA: Anything else you want the Lawyer to know before I connect you?
Customer: no