The second link answers that question adequately, but if it isn't clear:
rajesh9pl wrote:I understand NHS will give free treatment in case of emergency .... What if she is not feeling well and want to consult doctor/GP and takes treatment?
I hope you know that doctors/GPs are also "NHS" (unless you wish to visit one who has a private practice). And that doctors/GPs usually do not provide "emergency" treatments, but walk-in centres may. In other words, every consultation / treatment other than "emergency treatment" at medical treatment facility equipped to provide such services is to be paid for.
Google to look for "travel insurance" available in the country your relative is coming from, as visitors cannot purchase travel / medical insurance in the UK.