Her blog does indeed say that she
can cook and even expresses some mild interest in it, but I think it also mentioned that she doesn't get to do it very often. She even goes as far as to stab at the "anime stereotype" that girls like her can't cook. The scene never actually demonstrated any awful cooking on her part, just a general klutziness with her hands, not to mention how very troubled she was at the time. It's more that Alto recognizes she's a bit off her game, probably because she's not feeling well anyway, being a bit of an ill girl at that point.
At least, that's what I took from it, though before I read that blog I did read that scene as indicative of "can't cook". It does seem to fit, given her glamor lifestyle prior to that moment.
I still want to know what was in that champagne.
Hi, BTW.