Hi Hannah,
I have had some more info back, with this dinner in mind
Some of this might be a bit late now, but I'll tell you anyway.

Here's a few details that should let you know you're on track
"little black dress, not ball dress, knee to calf range"
"anything with a tight waist uncomfortable, because you will be sitting down"

Jewellery - she'd go for single pendant or single string - not too showy if you want to blend in
Makeup - enough to know your're wearing it, but not too much (less than an American might wear to a similar event)
Hair - wear up
She suggested a velvet jacket might stay on better than a scarf/pashmina during the long meal (probably too late for that though)

Hi Anne,

Thanks so much!

OK, let's see:
little black dress of the right length - yes, mine is between knee and calf (it is Sophia dress from JCrew in black silk)
tight waist ... hmmm ... it does go in in the waist, but it is not uncomfortable, so I think it is ok
Jewelry - have pearls necklace or a diamond brooch, or, as Shiny suggested, the brooch clipped on the pearls - I guess for "not too showy" I will just go with the pearls
Makeup - I never wear too much, I actually wear too little usually I planned to put on only mascara and lipstick, I guess it is ok. I am in Europe a lot (conferences), and my makeup is usually in line with what women wear there.
Hair up - oops ... I guess I will go with a tight french bun then. This is the only style of hair up that I can do myself. I also can do "half-up, half-down" but it seems not formal enough.
The only velvet jacket that I have is purple, so no I guess I will go with the pashmina and try my best to prevent it slipping from my shoulders.

Thanks again, you are the best!!

Hannah, did the J Crew dress work for you? Did you post a picture somewhere and I missed it? Hope you have a great time at the event! Take pictures of your final outfit for us!

Dani,

So sweet of you to check!
Well, the JCrew dress is the right size, however way too much cleavage. I am now looking for a black silky cami to wear underneath. I have a black cami, but it is not the right shade of black (although, in the evening it might not be noticeable...). When I have the right shade cami, I will definitely post pictures!