Hi,
I feel that it is better for weight gain to come from healthy fats rather than saturated fats (like dairy). So, I would suggest foods like nuts, seeds, avocado. Does she like almond butter? Or sunflower butter (made from sunflower seeds)? I grind up linseeds and chia seeds in our coffee grinder and sprinkle them over cereal. This is any easy way to get seeds into my kids' diet.
Have you looked at the non-dairy alternatives to cheese and milk? You can buy non-dairy cream cheese (Tofutti brand).There is a brand of non-dairy spread called Nuttelex.
Good luck.

ETA I have just realised you are in Sydney. You will have no trouble finding non-dairy cheeses - look for Cheezly brand. Tofutti also make non-dairy sour cream and sliced cheeses. Check out an online store called The Cruelty Free Shop for lots more dairy free options/ideas.