I wanted to let you know how sorry I am that this happened to you. It must be so heartbreaking to order something and have it completely not as advertised. I have cosplayed Aerith myself and I understand the appeal of the character.
My personal feelings are that the "new" dress that you have found is too dark and will not look right, particularly when you add her trademark red bolero jacket. You will likely not be happy with the results.
For the original dress, does it fit at all? If the basic fit of the dress is alright, you might be able to take it to a tailor who specializes in women's clothing to alter the neckline for you. For the shoulder straps, spaghetti straps are pretty, but not completely necessary. When I made my first Aerith dress (I have remade the costume once already), I used a jumper pattern that did not have spaghetti straps (http://kwiksew.mccall.com/k2836-prod...play&list =0)
. I altered the pattern slightly so that the seam between the top and bottom part of the dress was eliminated. I also changed the neckline a bit so that it was more of a v-neck than a scoop neck. It wasn't perfect, but I was pretty happy with the results. Your jacket will cover the shoulder straps, so the shape might not be as important as you think (at least in my opinion). I have some photos of it in my gallery and you can see that while it isn't perfect, it still got the job done.
As for the jacket, I think that if you might be able to fix it. If you have any comfort using a sewing machine, you should be able to add a hem to each sleeve right underneath where the straps are. Judging by the photo, the straps seem to be where they should be, but the sleeves just extend too far past that point. If you are not comfortable with this step, I think that going to a tailor to hem the sleeves is a good bet. Hemming a garment is not overly expensive and can be done rather quickly.
I have also found some good cosplay stuff in thrift stores. If the dress does not fit at all and you need another one, you might be able to find something that you can work with for your cosplay.
I think that the jacket should be the primary focus, because it is worn on the outside and if it is done properly, it can really help the overall look of your cosplay.