Can you give us an idea of what is a definite no-no & what features heavily in her diet? It will give us an idea of what will be available eating out & in the supermarkets. Then we can help you with some choices of where to go & on what basis. I would always say self catering anyway in Greece, regardless of whether a special diet is involved or not.
Where would you want (or be willing) to fly from? Some places only have Gatwick & Manchester as options, the more touristy & heavily visited islands will have options from regional airports.

Thanks for response - to reply.

When I say strict diet I mean organic as much as possible. Our usual at home eating =

Breakfast = organic fruit ( no chemicals / preservatives / fruit on steroids)
Usually followed by organic oats with nuts, seeds & dried fruit & cocoanut milk

Lunch:
Organic veggies juiced
Organic salad

Dinner:
Organic vegetarian dishes
Whole-wheat pasta

Looking to fly from Gatwick

Many thanks

Although a huge amount of fresh veg & fruit is available here, as well as many vegetarian dishes, I really don't know how much of it is organic. You do see some sold as such, & therefore higher priced, but it's possible that some in the ordinary fruit & veg shops is more organic than your usual Tesco, Sainsburys etc produce, especially in the smaller towns & villages in agricultural areas. The problem will be that the seller often won't be sure if, or what, treatment any crops have had, for instance our local shop buys from all sorts of local farmers, so it would probably be a mix of those that use chemicals, those that don't & those that are truly organic. We sell him some of our lemons sometimes, they are so obviously different from his other main supplier, ours are straight off the tree, neither the soil nor the tree has anything other than water on it!
It's a tough one, & without some research I wouldn't like to say what would be readily available as truly organic. As far as I know there'd be little or no fruit or veg with preservatives or steroids.
Many nuts & seeds are also readily available, again I've never checked as to whether these are organic or not.
In this area I know wholewheat pasta is not a problem, we have a shop where all pastas are made fresh on the premises. As pasta does feature quite heavily in the Greek diet in many areas I don't think this should be a problem.
Eating out vegetarian dishes, although I'm not sure how many will be suitable because of the olive oil:
Yemista=stuffed, (with rice mainly) peppers & tomatoes (olive oil used)
All manner of salads, usually with olive oil on, but you can ask for it with nothing on & add oil, vinegar or lemon if you want.
Various dips (some are pureed veggies), melitsanasalata, which is aubergine dip, again with oil in it. Tzatziki: yogurt, cucumber, garlic.
Fried cougettes, aubergines etc
Some idea of ingredients here,
http://greekfood.about.com/od/vegetarianrecipe1/tp/bestvegrecipes.htm
Many things have oregano sprinkled on them too.

My advice would be to have a written list of main choices, things that would be ok, & things that are definitely nots, especially as far as some of the ingredients are concerned. Have it translated into Greek & carry it with you, for shopping & eating out. There is an excellent site that does this for all kinds of diets & allergies, if I can find it I will post the link for you.

i'd say in traditional tavernas a good deal of fruit,veg and meat comes from local sources and they dont tend to rely on the same chemicals we need to make things grow bigger in colder climates in northern europe,that said i'd imagine it's difficult to grow most things in the med without insecticides of some kind due to the amount of bugs that go hand in hand with hot climates and fertile soil

I know the restaurants by where i live use fresh veg grown on the island where they can but as with anywhere it comes down to cost effectiveness and the famrs with the cheaper produce on sale probably use more chemicals ,but on the whole i'd say greece and in particular the more tradtional resorts are going to be where you get the most 'organic' food of all holiday destinations,whereas shopping in the local supermarkets tends to get you the same sort of stuff you'd get in tescos unless you go to markets and village grocers away from tourist shops.

Greeks live forever and are active well into old age,diet plays a massived part in that i'd say

I found the site I was thinking of,
http://www.selectwisely.com/
Their standard cards are mainly regarding allergies, but you can stipulate whatever you wish to be translated if none of those cover her needs.

Just like to say a quick "thank you" to you folks that have replied as you have offered really great info and a sense of concern for our situ -

I appreciate that - very much

Have a lovely day