Hi,
Our daughter is almost 8 months now, DDF508, pancreatic insufficient. She is making good weight gain (docs say better than expected!) and is currently around 7.5kgs. I'm feeding her breast milk first (her favourite, and has excellent calories, overall nutrition and easy to digest). Additional to this she loves tasting different foods- any fruit or mashed up vegetables, and sometimes meats too.
After doing a lot of research I have formulated a drink for her that is in a base of rice milk and includes coconut milk or coconut cream, avocado, spirulina and a pinch of salt. You could also use nut milks as a base. This is very nutrient dense, has lots of calories and is easily digestible. Our family has multiple problems with dairy including excess mucus production, so I'm not introducing it to our daughter at this stage.
I think to get her most interested t is good to let her 'play' with food and not be too forceful with it.
Good luck