The vet did an xray and didn’t find any blockages. It turns out it is pancreatitis. She got into a brick of brown cane sugar (not sugar with molasses), and apparently that much sugar all at once for a dog is very bad, especially since she’s 10 years old. We were sent home with some probiotics and instructions for her to eat a bland diet for a few weeks. The vet said she will be fine.
My childhood dog once ate a dozen chocolate cupcakes off the counter to no ill effect whatsoever (aside from the scolding we gave him for stealing). We were surprised, to say the least.