Petunia hasn't even touched her third bottle for the past couple of days. (I usually send four bottles, of which she usually drinks three.)
She has been eating solid foods for about a month, and she has recently really ramped up her intake. So maybe she will drop down to drinking less milk consistently, and I won't have anything to worry about.
Or maybe the last couple of days were just a fluke, and next week she'll be back to sucking down three or four bottles a day.
So thanks for all the great tips in the comments to the last post, but maybe I won't be needing them, after all.