I love the way fussy eaters and McDonalds always end up being mentioned in the same breath.
As a mum of the fussy eater, I've been seduced by the ease of crackfood. Quick, easy and the nearest to potato mine would ever get. I soon realised, however, that her 'habit' was going to wreak havoc with her future, especially as she was becoming quite fond of a Maccie D's on a regular basis. So I swapped, over a period of months, diced chicken breast (free range of course) for chicken nuggets and roast potatoes (in olive oil) for chips.
DD still loves a Maccie D's occasionally, though and I use it as a treat, usually during the holidays, when we go to the pictures. It's still one of the few foods my daughter gets excited about That and ice cream And she's lean and active, so I try not to worry too much about the odd imbalance.
Ormirian I think that most parents feel guilty about not feeding someone else's child when they're in our care, BUT most parents with fussy eaters have had to get used to it. You have to do what makes you and your daughter happy on her birthday. You sound like you'll be responsible about the fussy eaters feelings, but that doesn't mean you have to pander to them. Like becs said, you can keep it all low key and just make the child feel as comfy as possible. Outside of that, you have no obligation.
Enjoy your day, your wine and olives...