What does your daughter suggest you wear? If she comes back with something suitable for a teenager you know you can disregard her opinion.
I think it's fine. It's not the most exciting or fashionable dress, but it's completely suitable for the occasion and you will absolutely blend in.
One thing I wondered, though, was whether it suits your colouring? That might be why she's saying she doesn't like it? And do bear in mind that while you've put on a bit of weight, many women in their 40s would be delighted to be a size 12 and would be wearing something to show it off. I'd love to be a size 12!