Now in line with yukkuri characteristics, we ask the following questions.
1) What is kogasa filled with? 2) Is the umbrella a separate yukkuri that's very attached to kogasa or is it kogasa's accessory? 3) Is the umbrella edible?
1) Apparently the character it's based on is a ghost/spirit or something. Perhaps artificial sweetener of some kind, instead of a real food as they're based around "fake" people...? 2) Accessory seems more likely. Its own thing in place of a hat or ribbon etc. 3) For other yukkuris, some stories refer to accessories being edible. In others they're not, so it's up to interpretation.