I called United and the really nice woman (I foresee a gushing letter to United) looked at the record, put me on hold for quite a while to confer with her supervisor, and then re-instated me on the original flights. I'll be getting home a bit later, but at least I won't get a really nasty surprise when I grab the puppy (now 26lbs) and head off for the airport.
PS: Gail tried both the regular-flavored milk substitute I got at Clark's and the white cheddar-flavored type. Hopefully between the three there will be enough of something she likes to give her at least some nourishment. Baby food was a no-go.