Sorry hijack OP- but your dh's aunt sound like my MIL
When I got married (24 years ago!) it was quite traditional-but on the cheap. (dress "run up" by a local dressmaker, homemade invitations, cheap venue, homemade buffet, all my relations were happy to bring a plate) My parents paid, but they are not loaded and set a budget and we stuck to it. I was 22, dh was 23.
MIL had a catsbum face the whole time. It was traditional for my parents pay, so she let them (she only paid for the cars- because that's what the etiquette books said the grooms parents pay for). She wanted to have the reception at this very naice hotel which was well out of our budget. She was appalled that I contacted the bride getting married immediately after me at the church to split the cost/agree on colours of flowers at the church.
Breaking point came when rather than waste money on morning suit hire, dh went and bought a new suit that he would be able to wear to work afterwards, for the same money. He was letting her down, and to remember it was "his wedding too", and she has never got over it.
23 years, 3 kids later, she still thinks he married beneath him, has no interest in our dds. Would have been different if we'd had a ds I think, dh is the last one with our surname, she is always lamenting how the name will "die with him".
She spends so much time bigging up their family - dh was brought up thinking they were upper middle class (tea and cucumber sandwiches - the whole thing), and such a huge deal is made of "Family", I am not "family". DD1 is now she's 18. DH did some family history research- go back 3 generations and they are all coal miners and labourers. He even found a direct ancestor listed on the census as a "pauper" plus someone who was sentenced to hard labour for petty theft. MIL refused to believe him.
When dd1 got into her first choice uni, dh phoned to tell her, and all he got from her was "you should have gone to Cambridge, you should have done better etc etc" (Dh did get an offer from Cambridge but didn't get the grades- she's never got over that either )
I have a senior volunteer role and met a senior royal last year, she had a catsbum face about that too. Keeps going on and on and on about her 'lovely" neighbour who did a similar role for a few years in the 1970s (I've never met neighbour)
We do actually quite enjoy being a disappointment. DH is now fairly near the top of his profession at 44, dds are doing well (one at uni, dd2 doing GCSEs this year etc), I'm back at college doing teacher training, nice house - we like to predict where we will disappoint next - it's MIL bingo.
Sorry to hijack OP- I hope you have a lovely wedding!