My fashion dilemma

In a couple weeks, I'll be going to an ESA convention where I will need to wear a formal dress. Sounds easy, right? Wrong. Because I have to wear a formal dress that is 1. floor-length and 2. Pastel, but not sage green. These are the rules. Every year, someone gets to dictate the dress code for officer installation.
The problem is that floor-length dresses come in three varieties: 1. Bridesmaid 2. Prom 3. Mother-of-the bride.

Last year, I went the prom route. (I had a 'jewel-tone' directive) The dress looked pretty but it was obviously a prom dress and I worried about looking like one of those women who refuses to dress appropriately for her age. So earlier this year at an ESA function, one of the ladies told me that a bridal store down the street put some of their mother-of-the-bride dresses on sale for $50. My friend and I went to check it out. Among the chiffon pallazzo pant suits and beaded muumuus, there were a few tasteful dresses. I found a pink chiffon dress with a rouched bodice and cap sleeves that my friend swore to me did not look too matronly. I tried it on and it was big in the waist, but the salesgirl clipped it together in the back with a clothespin and told me that with alterations, it would be lovely. So I bought it. I told myself it was age-appropriate and it would never be confused for a prom dress.

Last weekend I realized that I have less than three weeks to get ready for convention. I called a seamstress that my friend recomnded but the seamstress had retired.

And so I googled around for a tailor in my area. I tried my dress on again, and although I am doing all I can to expand my waist, it still didn't fit.
Since my new dress was hanging right next to last year's dress, I was reminded that I should take last year's dress to the consignment store. The ladies at the consignemnt store would know of a good tailor!
I packed up both dresses and a pair of high heels and headed to the store. I told myself that the heels were because the tailor was going to want me to try on my pink dress with shoes so that she could make her markings.
I walked into the store carrying the red dress, which I put on consignment. I asked about a tailor. The shop girl told me about the tailor they use, but I couldn't really pay attention to her because in the back of the store on a headless mannequin there was the most gorgeous dress I have ever laid eyes on in person. Strapless, hand-beaded bodice with a gorgeous chiffon skirt, and pink. I was told it was a size 8.
This is an expensive dress, I told myself, so it's possible that it's an expensive 8, which is really a 10. I tried it on, but only half of me fit into it.
But.
There was another dress, a prom dress, brand-new, floor length and pink. And so I tried it on (lucky I had those shoes!) and eventually bought it. I have no idea how much dress alterations cost, but in that dressing room I conviced myself that alterations on the first dress would probably cost almost as much as this second dress, which made my boobs look good.
And so I brought the first pink dress into the store to put it on consignment, and the shop girl said it should probably go to their sister store for mature women since it is such a beautiful mother of the bride dress. I dont know if she did it on purpose, but the instant she said that any trace of buyer's remorse I had instantly vanished.

So now I have a perfectly lovely prom dress to wear, which would be fine, except that I am 37 years old. I'm too old for prom dresses and too young for mother of the bride dresses.

I found plenty of truly age appropriate dresses but they were all the wrong length, oh, and black, because I am an adult.