Any shoes that match the color will work. White would be the easiest default rather than color-matching
Given the location and time of year, I would hope the wedding is inside, or at least under cover. If its inside, a raincoat would be appropriate to wear over it, and if they planned accordingly they should have a coat drop-off once you get inside. You could also wear a cardigan (White skintone, or black could work, or if you can get the color-matching right, light purple would look amazing with the subtle shade of the flowers). But if you did choose a cardigan, as would be needed if its outside and just
covered or even if you just want a shoulder cover once you're inside, you would need to plan for your hair, which you probably wouldn't want to get wet. In which case you would still want to walk in with a coat over it (doesn't need to match, since its for cover and not part of the outfit and should be removed once inside) or with a hat. But if you aren't good with fashion I would probably forgo the Hat, since it's really, really easy to ruin the vibe and throw off the whole outfit with a weird hat lol.
