((((HUGS)))) it's so hard. I LOVE my MIL (actually closer with her than with my own mom in some ways) but she just doesn't get food intolerances at all. We are waiting for some results back ourselves, actually and I'm suspecting a wheat intolerance and/or lactose, among other issues. We already know he reacts really badly to pumpkin/squash (hives and up all night with tummy pains), coconut (hives), pineapple (discomfort) and other unknown items. Certain pizzas make him up all night with an upset tummy but others are OK. She doesn't get it. AT ALL. It's a bit easier for her with my niece since she has an anaphylactic reaction to nuts and she "gets" that more, even though she is totally confused by the whole "made in a factory with."
My DH is also a bit clueless this way. Until he has concrete evidence, he has a really hard time admitting a reaction. So even still he tries to argue the pizza reaction, even though it's happened a few times in a row from the same place. At first he'd say it must have been from teething or something else. He's starting to come around, though if we have to go gluten free or something like that (won't know for 2 more weeks probably) he will have a VERY hard time with it.
Anyway, stick to your guns and tell them you appreciate their thoughts but you are doing this a different way. IF you want to up the calories and good fats in her liquids I'd definitely go with adding some coconut milk to her almond milk but that's up to you. But at least that's a natural good source of real calories as opposed to an empty and often hard to digest filler.
More HUGS!