Fortunately, she did so all in one place, and right while I was watching, so I was able to catch her (priority #1) and contain her in the bathroom (priority #2) before cleaning up the mess before anyone could step in it (priority #3).
She has been announcing her displeasure at being not only sick, but locked in the bathroom, loudly.
Now that the howling has died down, I think I can maybe go in there and change out her litter (before she threw up, she had some digestive nastiness from the other end) and deliver a bowl of water (versus the toilet, which is her favorite anyway) before leaving her in there for the night.
*Yes, I know cats don't have crops.