I'm not quite sure about that. The point is that because she rejects one food in favour of another shows a preference, but it does not necessarily show an understanding of exchangeable value. To say it shows she understands how to attribute value I think is jumping to conclusions. I'm not saying it's impossible, I'm saying let's not jump to conclusions about what's going on in her mind. She could say that she prefers cans of tuna. That doesn't mean she is able to think that one can of tuna is worth 200 sausage snack packs to her.

edit: I suppose we could claim that the cat is making judgements on value, but is unable to actually measure the value they're thinking due to complete lack of mathematical prowess. I guess it's possible in that way for cats to understand value, but not actually use or express it in any way, except for choosing whether to eat what's in front of them, due to lack of cognitive capacity. Perhaps I was guilty of thinking value judgements require mathematical understanding.