Congrats on the weight loss.
The Kate Middleton dresses are great. The one you posted, even if longer and maroon, is a no go because of all the lace peekaboo going on. Nothing to do with the bride or her feelings, just looks tacky for a wedding, fine for other occasions. Even if it's not quite as bad as that, it's seems tacky. Without the sheer lace stuff, fine.
A summer wedding gives you a chance to wear florals, pastels, floaty, lots of things that don't work in colder months. You might want to take advantage of that.
Bodycon, if the dress is advertised as that, probably Means a dress for clubbing, and you will stand out as tacky at a wedding. It may shout look at me, and perhaps that was what your mom meant. But if it's more like the Kate look, go for it.
I doubt your friend will care as she will be caught up with being the bride. Why not ask her or other good friends who can actually see the dress if they think it's wedding appropriate?
Of course there are weddings where tacky is the norm, then it won't matter what you wear, but elegant is best for a wedding, not body con. Elegant can certainly be figure hugging, because it's cut well. Quality fabric, no mesh panels or peek a boo, no plunging necklines even if covered with lace.
Buy a few nice dresses! You deserve it!