Tbh you're not in that bad a situation.
You have meat potato and 2/3 portions of veg (leave raw if that what she prefers), non of which need to be branded. That gives you one or 2 well balanced reasonably priced meals a day. If you get away with it, add whole milk, butter and/or cheese (make sure it melts in fully) to mashed potato to bulk out calories. You might well find you get away with steamed veg much easier than cooking them by any other means. Make sure it's a full 80g portion of veg every time.
Do you have an electronic scale with a tare function? You will get the same consistency in rice by measuring the rice and boiling water then cooking on low until the water is absorbed. You may find a rice cooker actually pays for itself.
Does she eat porridge? (Buy the cheapest oats) the electric scales should give you consistency here too. Porridge again is great again for hiding calories with whole milk, or your prepared apple. What about egg? Scrambled or otherwise? Again good for the whole milk trick
Have you tried adding crumble to the pureed fruit? Would she tolerate something like a basic Victoria sponge that could be baked ahead and served as dessert to bulk calories. Both of these are good for hiding butter.
When you're bringing something new into the house, dont get the branded one. Make it a binary choice, either way eat it or dont. Keep it as an option even if it is initial rejected.
You may not get a wide variety in her diet but actually it doesnt sound like a bad diet or one that has to be overly expensive. You have meat, veg and potatoes which is actually all you need for a balanced diet. Bread, jams sauces really arent necessary. It sound like she mainly isnt keen on the texture on anything processed (bread, pasta), possibly stuff that mixed together(sauce) and slimy stuff (jam, possibly pasta).