Daily poo in pants (often more than once) - tick
Just learning to use an open cup - tick
Fussy eater - tick
Only uses a spoon (and specific ones for specific meals) - tick
Only eats from a bowl, not a plate, and food must be a mushy texture.
Won't try ice cream or chocolate - tick
My 3 and a half year old DS has Aspergers and sounds quite similar to your DD. We've just had the added joy of Pre-School Booster jabs setting him back with his eating and tooth brushing.
Anyway, we just go with it all. Buy cheap pants and chuck them rather than soaking and washing etc. We're about 3 months in to potty training and I'm expecting to be binning pants for some time yet.
He's made real progress with drinking from the open cup (and it doesn't always have to be the same one - yippee!)
The EarlyBird course from the National Autistic Society was useful at giving us some perspective about the fussy eating. They told us that if the child was growing well and getting enough "fuel" then it was ok to go with the fussiness. I guess the using a spoon thing isn't a problem if it eases the stress of mealtimes. He didn't use to bite with his front teeth, so had to have everything in small pieces, but now does bite and has a sandwich cut into 4 rather that 16, will bite a biscuit etc. Sometimes, I feel with our son we need to focus on just one thing and expect it to take ages, and it will happen in the end (if we're lucky).
Also, our Occupational Therapist suggested having a "learning bowl" where they have exactly what they want to eat on their plate, but you have a separate bowl of other food (maybe take a spoonful out every time you cook something and sick it in the freezer to have as play food)to play with/poke/stir/wiggle your fingers in/whatever to get them used to different colours and textures with no pressure to eat it at all. Hopefully, over time you can persuade them to try new things (disclaimer: haven't tried this too much yet, too much else going on!)
Wishing you all the best,
DB x