As the many comparison sites and photos will attest, she definitely had “work” before the wedding - nose, chin, dental veneers (which alter the shape of your mouth), as well as losing a truck load of weight.
It doesn’t appear she has had more surgery, but she definitely does the botox and fillers regularly (I probably would too if I could afford it!). Plus, she is (or was) a smoker, which is not good for the skin. I just don’t think she’s ever been all that attractive, really, so it would take a LOT to make her so.
Mary also had her eyes done prior to the wedding. If you look at pics of her during her first year in Denmark and prior years in Oz, her eyes had hooded lids like her sisters. By the time of the wedding, though, she had big doe eyes. Then a few years later, something happened and her eyes went wonky. One became smaller than the other and the doe eyes disappeared. I think the nose job happened before she moved to Denmark. Teeth straightening happened after the wedding.
I haven't noticed plastic surgery since. But definitely fillers. Her cheeks flatten and inflate regularly.
She was never very pretty, but she had youth on her side in the early years. So in some photos from her earlier years, she was attractive. Now she has no youth, and she didn't invest in becoming a better person so she has nothing going for her now.