***EDITED TO ADD***
L., I hope I didn't come across as condescending. I didn't mean it that way. I figured that there was more to the story about why she got the sunburn, but you just didn't put it in your original post. There are days that I still get too much sun, and I want to kick myself for being so dumb. It happens. Hope she's not in any pain! I know how painful sunburns can be!!
Try a spray tan. I was totally skeptical about them, until I tried it. They do give you a nice color (if done properly) and look really natural and nice, in most cases, even on fair skin. It may not totally erase the lines, but it will definitely blend it so that it may be barely noticeable. I would recommend getting the spray tan the day before the wedding, if possible. And be careful because some of the color 'may' rub onto her dress. That's why I say do it at least the day before. Presumably, she will have bathed at least once by the wedding, and the bulk of what would wash or rub off would come off in that first bath. You could do it two days before, but in truth, they don't last very well, so two days before is as far as I'd go to ensure there is still some of it left by the wedding. Water is definitely something to avoid with a spray tan if you want it to last, so I'd avoid swimming after she has it.
And I know this goes without saying, but as a fair skinned person who was allowed to get sunburns as a child (before anyone really knew how bad that is for us), please don't let your daughter get sunburns! I've had countless moles removed for containing abnormal cells, and four of those had progressed toward melanoma, and had to be surgically excised, leaving me with depressions in my skin where they took the "chunk" of skin out, leaving rather unsightly scars as a result. Sunburns aren't nice to us. :)
Sorry for the soapbox, but I know from not nice experiences that we really need to protect our kids from sun damage.
On the other hand, I hope the spray tan works for you!