Offer her food and water and she will eat what she wants. You may need to tempt her with some cooked egg if she turns down the feed. If there is no serious underlying issue, she should respond fairly quickly to the miconazole.
You don't need to wait for a full crop in the morning to treat for a yeasty crop. During fall molt, a slow crop is not at all uncommon. Molt can hammer a chicken, disrupting appetite and crop function. My flock is especially mopey right now, and I've been treating one of my oldest hens for sour...