i'd say it's fine, elderly cats usually can do with getting more nutrition, and if she likes, why not?
i have a bunch of leftover KMR 2nd step, i still dole it out occasionally to my cats as a treat. they get so excited when they hear me mixing up the powder
Cats love fat & cream, for many of the same reasons people like it. But cats, like people, are not good at processing lactose. Goat's milk is much more like human milk, but it's more sour (like human milk) which is why it's less popular. Anyway, while a human can eat ice cream and be gassy and uncomfortable, a cat will take it much harder, so definitely stick with "cat oriented" milk if you want to offer it up as a treat.
However, since it's not as tasty as cow's milk, your cat may not be into it if she's never had anything like it in the past. I'm not surprised she's not to into a new food item. Just remember that if she does get into it, milk counts as a food, not water.
She's holding it down but I think it's affecting her behaviour. Before I let her have some she would come in and not be racing round the garden, but she races round the garden and won't come in since I started her on the milk, so I have to go outside, catch her and carry her back in. I think the milk makes her hyper or something.
Is that actually possible for a cat to go hyper thanks to the food or drink it's having?