Most brides do a trial run of their preferred hairstyle/updo with their veil prior to the wedding. There's no way she could have sat through one and said, "Yes, this is how I'd like my 'hair' to look on my wedding day."
I'll bet Mary did multiple trial runs of the whole ensemble because she just couldn't believe she would be a royal bride (along with Grace Kelly, Lady Di) and she wanted to admire herself.
Considering she has sported similar bowling ball hairstyles many, many times since, I'd have to conclude that she likes the style. Mary is just a big ball of bad taste.