I have watched my brother go up being as bad as what you are describing. Honestly. It has traumatised my mum so much she is now unbearable to be around when I'm trying to feed my own children, one of which is probably as fussy as yours.
She ACTUALLY took dd1 to the gp for a routine thing at my request, but ended up mentioning she thought she was malnourished and the health visitor called me up for an appointment!!!
My mother was advised by paediatrician (and backed up by dr. Spock!),
To just give the things he liked. He pretty much lived on fish fingers or sausages with chips, boiled eggs, bananas. HONESTLY. She did it, but it still worried her senseless inside. [mind boggles as to why she is now in a spin about my dd]
I had the healthiest appetite ever and ate everything.
Now he has the healthiest diet and I'm a terrible snacker etc. He will literally eat anything now, in adulthood (except eggs).
It's SOO hard to make it a non issue. My problem is that my fussy eater is now having a bad influence on my better eating younger one.
I have to try and keep toddlers diet varied at lunch time and just stick to the same old pasta in the evening.
I really believe that if she is getting the right nutrients then why make your life so hard for yourself. It's boring, but just make the same old.
It makes it really difficult to keep the rest of the family happy, but I'd rather that than force her to try things and have her gagging at the table (that has happened).
Food is something to nourish us and you don't want to create bad associations with her and food.
I have cried at mealtimes. I used to have to walk away from the high-chair and hide in the kitchen to compose myself.
Because of that I feel very very very strongly about this.
Look at it this way pasta = carbs, tomato sauce - veg (any chance of mince in there?), yoghurt and cheese = protein and dairy.
There has been this massive push in the UK over the healthy eating, wonderful 3 yr olds eating salad, vegetables etc etc....
I feel like a failure because my child doesn't.
But I made a conscious decision not to let this put pressure on me.
I'd rather she ate a head-bangingly repetitive diet with a good balance than feel that she has to eat broccoli and oranges just like my friend's child.
Incidentally she has started reception in a 'healthy eating' school,
And I almost fell off my chair when she took a piece of cucumber from my salad and ate it - Seeing how her peers help has given her some insight in to how limited her diet is - not that it is helping much with the variety, but it was a small step for me.
(my friend didn't quite get why I was so excited that she was eating cucumber)
I'm sorry, I know this is a long post, but you can't imagine how strongly I feel about this, I do know exactly how you feel but that was my way of coping with the situation. (Meal times are actually quite pleasurable now)