wendy - everything you describe is what happened to me with Alex. she is not spirited (liv is and never had this extreme an issue) but was textbook / angel.
up until 2 1/2 she ate like a champion (coudl live on avocado sandwiches, licked brie off crackers, stole african curry from my plate) between 2 and 3 1/2 we lost foods here and there but i did not notice as i was still dealing with PPD and dealing with 2 kids at very different stages.
we moved when she was 3 1/2 and it went rapidly down hill from there and now at 8 we are still dealing with this. i don't think we are friends on FB (?) but i have posted a lot on there about my frustrations over the years reachign a head a couple of times including 2 weeks ago. Alex has THE most sensitive pallate i have ever seen (to taste, texture, any deviations from what she knows something to be). if i sub a brand of PB in her sandwich she wil know at first nibble, she can tell the difference in a fish finger by sight even though it looks identical to every other person). the foods she cut out were all mentioned in your earlier post - berries, apples with skins, meats, veg etc with a preference for carbs (mostly healthy ones but still restrictive). her current diet (without my sneaky chef style baking) is 1 banana daily (i refused to let her have 0 fruit so she chose to keep bananas under protest), healthy cereals (we don't do sugar ones), real porridge with a little honey, peanut butter (on crackers, wholemeal bread or a bagel), fish fingers or crumbed fish, shredded mozarella cheese (can tell if i accidentally buy full fat), homemade mac and cheese, plain pasta (not even oil or butter on it) or rice, hashbrowns, quesedilla (made with wholegrain tortillas and said mozarella)+ snack foods (meusli bars as healthy as i can get, popcorn, pretzels, etc). I DO get extra nutrition in by working with her carb preference and she loves beetroot and cocoa muffins, pumpkin pancakes, pink pancakes from deceptively delicious, etc.
i think aisling's first post summed up what i wish someone had said to me - keep offering the foods even if rejected 20 times. i never made/make her eat anything, but i DID stop offering things over time and catered to thiese preferences out of respect i thought because she seriously woudl get hysterical at the THOUGHT of some foods (if she knew chicken was for dinner she would start stressing about it and crying at 2pm). i thought it was related to the move so kept "riding it out", but it IS frustrating to deal with for YEARS (been 4 + years now with both of us crying a LOT). i hope you (and anyone else reading this) do not have to face that kind of time frame and do think the main thing i did wrong was to not offer the foods more often - i would still put whatever veg liv was having on alex's plate too, but so many meals were just what she liked instead of soem of what she liked and some of what had been rejected.
we ended up at a nutritionist last year and the method she advocated was similar to kate's - put out al the food and always include 1 or 2 of their preferred foods but they cannot just eat an enormous amount of 1 of those (ie can have 1-2 normal serves of plain pasta but not 2 giant bowls and nothing else. so once she has had enough of her faves it is try one of the others or meal is finished). never to force them to eat anything (so she stood by my never making her try even one bite) etc
sorry for the long post but i look at you like it was me all those years ago and i don't wish this hell on anyone. i wish i had friends like aisling did who said what they did, maybe my stress levels would have been less and my child woudl not feel so badly about her "difference" every time we are in public, at a BBQ, dinner out or travelling!
hugs to you and Finn!