I've had a lot of people asking, 'Can I borrow [food item]?' I normally answer, 'No but you can have it. I really don't want it back when you're done with it.' Pedantic, I know, but 'borrowing' a consumable drives me right round the bend.
Sioteh Cat, good for you. I'd talk to your bather and let her know that Mooch is likely to ask for bows. Just so she can be prepared to say no or to charge a price that she's willing to make them for.
To be fair, I think there is a legitimate use of "borrow" for a consumable item--specifically, when the borrower returns an identical or equivalent item, instead of the exact item borrowed. For example, Merriam Webster
gives the example of borrowing a dollar. Generally, if someone borrows cash, they aren't going to return those particular bills to the lender; they are simply going to give the lender the same number of dollars that they borrowed. Likewise, it would be possible for someone to borrow a food item, consume it, and replace it with an identical item once they get a chance to go to the store. In a looser sense, there's the idea of "borrowing a cup of sugar" from one's neighbor. Of course, they're not going to return that specific cup of sugar and they might not return sugar
at all, but there's a implication of reciprocity. One neighbor "borrows" a cup of sugar so they don't have to run to the store, with the understanding that they will be willing to "lend" a cup of sugar, or some flour, or some tomatoes, etc., when the original lending neighbor is in a similar situation.
Of course, the Bow Moocher isn't borrowing bows in any sense of the word, because she is offering nothing equivalent in return. If she made her own bows (or fancy bandanas) of comparable quality to SiotehCat's, which Sio "borrowed" in return with comparable frequency, then IMO she could legitimately call it borrowing. And we would probably have never had a thread about it here because it would be a mutually-beneficial arrangement.