Why is she too old?! Yes, there are access courses for mature students but they won't always be relevant or the most appropriate course to take, dependant on the students plans.
Try being proud of her for going back.
People do all sorts of qualifications at all different ages. I have a friend currently doing her maths GCSE,in her early 30's, a friend, 35, just starting in some pre-accountancy type thing, and I'm also 35 and 'retraining' , degrees (BA and maybe MA) and career plans couldn't be any more different than my originals and the career is just a potential if my self employment isn't sustainable. Aside from that, my specific degree will assist me with several things as they are and cover skills I've either missed out on or lost, due to circumstance, along with boosting confidence.
So, studying can have various positives, plans and outcomes. How could you possibly decide what your niece wants or needs?
A little wave to @DevilishPyjamas .