Leaving aside Mana - which has just got a Michelin star and to which I havent yet been - there’s really only two places for a high end tasting menu. Restaurant Mcr or Adam Reid at the French ([Manchester, city centre] Adam Reid at The French - #13 by Harters)
Food is very good at both and this may come down to which location the aunt might prefer. Restaurant Mcr is very modern and in the buzzy Spinningfields area. Adam Reid is at the iconic “French” at the Midland Hotel (where Mr Rolls and Mr Royce first met) and is a sort of modernised Art Nouveau style. One of the things I like about the French is that dishes are brought to you by chefs, not servers, so you’re often getting the explanation of what it is from the person who just cooked it. But you’ll be fine at either.