aquagran
Ahhhh! Vintage…stylish! Definitely not poor.
I think you are being deliberately unkind, for some reason. To suggest that 'vintage' is automatically stylish is simply snobbery. It may be, or it may not - it depends on the dress and the wearer, not the age.
Wearing something more than once is not a sign of poverty. As has been pointed out, the RF do it all the time.
Having to buy cheap and getting something that can only be worn once because it's worn out is often all that people in poverty can do, as long-lasting clothes are expensive. The poor have to replace their clothes more often than the rich.
The OP has an outfit that is not only suitable for a wedding but makes her look and feel good. Not to wear it seems daft to me. If it matters (and I don't think it does) at least half the guests won't have been at the first wedding anyway, as they'll be from the bride's side or friends of the new couple. It will only be Shelflife's own family who will have seen the outfit, and if they remember a dress from 7 years ago, it will be because it made an impression, which is all the more reason to wear it.
I've just been thinking - I can remember what my mum wore to my wedding, but have no idea what she wore to my sisters, which was six months earlier. I don't make a habit of looking at my sister's wedding photos - who does?